Long term issues when someone with MH issues doesn’t get help and is sheltered at home.

In my opinion and from some experience of toxic families, your bigger issue is your DH. He is controlling the level of involvement his family gets to you, the access they get to your children. All you can do in these situations is manage yourself and protect your children whatever the best way that looks.

Just my opinion, you have much better clarity on all of the dynamics but leaving your DH is probably for the best.

You can have far more control of the situation if he only has the typical interactions divorced Dads get with their children particularly in Germany which comes across, at least, as a very traditional country.

How old are your DC?
You have to do a calculation:
How many more years until you are happy that DC will be able to look after themselves in this situation - perhaps their mid-teens?
vs
How many more years until one or both parents die and the crisis hits?

It may be that your DC age-out of the danger, and get to an age when they have the final say in how much they see their father and aunt, in which case you sit tight, carry on as you are, and keep your fingers crossed. As soon as the DC are safe you can think about divorce.

If the parents are likely to die sooner, your situation is much harder with no easy answers. When the DC get to about 9 or 10 years old they should be able to keep themselves physically safe (re. food, stairs, hazards, etc), but the emotional damage may not be preventable. It may be you have to divorce and have a court order about no contact with the aunt.

I am not familiar with the social care landscape in Germany.

however I can tell you that trying to get help for a mentally ill older teen/young adult is a fucking nightmare in the U.K. and trying to make the said older teen/young adult actually go to the help and do the therapy etc is a massive physical and mental strain.

going back to your situation, clearly protecting your children is the highest priority. Realistically the situation is likely to fall apart long, long before both PIL have died and there is any prospect of SIL living with you.

PIL will become frail and ill at some point. They will no longer be able to meet sils needs. There will be a crisis and the equivalent of social care will get involved. SIL presumably has no assets and relatively low income but is entitled to state benefits?

in which case I would imagine that once the first PIL gets ill - cancer or dementia or whatever - and her rules are no longer stuck to there will be a crisis, police may be called, someone will possibly be injured if she gets violent and state intervention will happen.

i think that chance of her making it through the illness and death of both pils without being forced into interacting with state support is low to nil.

so I’d stop worrying about her moving in with you because it isn’t going to happen.

in general you have more control over the situation if you stay married so this is the route I would choose (and did choose). How old are your kids?

You can’t control her but you can control your actions. I wouldn’t go to their house or allow dc there.
I wouldn’t invite her to your house.
I’d be clear to DH and pil she won’t be living with you in the future.
It’s their choice not to have engaged with services.

They will likely leave her their house as "she needs it" ... or your husband will just let her stay there

If you want to leave DH is there anyway you could get legal advice to see if this is possible with some kind of legal protection that he could have access but kids can’t have contact with the Aunt? Also how old are kids. This is a nightmare situation OP I really feel for you.

Could you sit down with PIL's and DH and ask what their thoughts are for SILs future?
Don't give your thoughts until last, if they have vague notions her moving in with you, you could give your opinion that SIL would never move in with you due to concerns about child safety. As a compromise you could suggest DH moves in with SIL - and see how that goes down with him! Everyone is kicking the can down the road, nobody wants to make a decision. I don't doubt for a moment PIL's will want you to house her - don't drift into that situation. You"ve got to make it clear it won't be happening.

This has to stop. You have admitted your letting your DH emotionally abused your kids! Wtaf! There's obviously much more going on with her OCD by itself doesn't necessarily make her manipulative, abusive etc she is too used to ruling thevriist and controlling others

Just read your update, I think separating from DH maybe for the best, but do undersyand your concerns re custody Im so sorry.
Your DC and your own peace of mind has to come first.
I do think SIL needs an urgent referral /reassessment.
It maybe possible to restrict her access to DCs if you were to separate by court order?? Not sure youd need legal advice.

You cant fix this.
SIL is ill and needs professional help and support.
I would be pushing ILs and DH to get a social services assessment and pyschiatric (sp) assessment.
Its good services are better in Germany than here so hopefully they can get help for her.
Its a very difficult and heartbreaking situation for your PILs.
My dad had serious mental illness and I used to live in fear of suffering myself and now I fear for my DCs, its not easy.
I know its hard but remember it is an illness not malicious but you are right to protect your DCs from it.
I expect your PILs are worn down and broken by it.

I think you might be overestimating what help could have been available - she is an adult and the circumstances in which she can be forced to be "treated" are limited. And try not to heap all of the blame on PIL. All of us are limited by what we can handle and in difficult circumstances people are reduced to just getting through to the next day. It takes resources beyond what some families have to deal with the "big picture" stuff, an it gets harder over time. It's hard enough with children but for adults the options are even more limited. Plus, more generally there is no point regretting or casting blame for the past. The only things that can change are from today onwards so concentrate on that.

I hope you do manage to find some more support for her and for the family.

You cannot see how she could manage alone but you definitely don't want any part in her care or letting her live with you. That is fair enough, she's an adult and is not your responsibility.

She does not have a learning or development disorder preventing her from doing normal day to day things. She may be too depressed or mentally unwell to do them though. But that's on her.

If she refuses help then she won't have any help. Sadly. Unless it gets to life threatening then she may be sectioned.

You need to just bring your kids to see their GPs when she's not there, or they come to you.

Just don't think about her and her possible issues once her parents pass away. As you say you are unwilling to offer any direct support in any case.

People are offering very good advice based on the UK - are you able to confirm which country you live in?

Just don’t go round there!
If the stair gate is removed or food your Dc can’t eat just keep your eye on them - that’s what parents have to do.
Why would she move in with you at any time? The woman has a mental illness, that doesn’t mean you have to pander to them.

What does DH think?
I totally see why you don't want your DCs mixed up with this woman, but you seem to be presuming that DH has or will have no choice but to care for SIL. It seems slightly strange that you are thinking about leaving your husband to protect you kids unless he has said he will move his sister in with you all. Even though he's her brother, he has no obligation to care for her.

My DB and SIL are in a similar situation. My SIL brother is a schizophrenic in his late 60s. He always lived with his parents but they have both died and he had to move in with my DB and SIL. Has never been able to work. Is tolerable when he is on his meds but frequently doesn't take them. My niece, my brothers only child, is the only family member left if my brother and his wife die. My niece has said that the day after their funerals she will be sending her uncle to live in a home/institution equipped to take care of him. She refuses to have her life overtaken by this because of poor planning for his care in the past.

I meant care assessment for SIL.

It’s called magical thinking.

The general advice is to not let the rules get more extreme. For instance, DD used to ask me, if I had cut the raw chicken and salad vegetables on the same chopping board? I was told to say to her:

”I am only going to say this once, and I am not saying it again. I chop the raw chicken, then I wash my hands, and do the salad on a different chopping board with a different knife. I don’t want salmonella any more than you do!”

PILs may not know what to do? I only knew, because DD1 was under Social Services for physical health reasons. (There are two aspects to Social Services - child protection, and the disabled). DH needs to discuss with PILs if they can discuss with SIL, if she would be willing to ask Adult Social Services for an assessment of need for herself.

PILs are legally fully entitled to say, they are not prepared to do any care of SIL any longer. There’s nothing Social Services likes more, than to put down the family will provide all care, which lets them off the hook. However, if the family refuse, or say they are only going to do x,y,z moving forwards, then Social Services has to assess her fully for social care.

As part of the assessment of need, SIL would have to undergo a financial assessment? If she were living in her own house, and needed carers to go into her house, she’s not entitled to that, if she has over £23,250 in assets, not including the house. There’s a sliding scale down to about £14,000 - if she has less assets than that, Social Services has to pay for all the social care. If as is likely, she’s not working and has no income/assets other than her benefits, then Social Services has to pay all the costs of her social care. She could ask as part of that, to be put on the housing list.

Then, regardless of what she does, PILs can ask Adult Social Services for a carers’ assessment on them. They are entitled to respite, and there should be a contingency plan for SIL, in case an emergency happens to them.

It is better for you and DH to get PILs to think about this now, rather than on the day of the death of the second parent. You would also be entitled on that day, to tell Adult Social Services, you are not going to do any caring of SIL, and she can’t live with you, so it’s up to them. Be firm. Social Services will do their best to blackmail you emotionally to look after her. No adult in England is legally obliged to care for another adult - the responsibility lies with Social Services.