AIBU to refuse becoming my mother-in-law's carer by proxy?

To be honest OP, it does sound like your DH is leaving all the hard work to his sister, she seems to be doing the bulk of the care, medical appointments, the cleaning, the washing and the food, while he sorts 'the admin' it's no wonder she is getting frustrated at him and is now approaching you to see if you'll pitch in.

I sympathise with her to be honest, the one closest in proximity is normally the one doing all the thankless tasks, it can be exhausting, she has expressed this to your DH and he is basically ignoring it from the sounds of it, he isn't really pushing himself as he has asked you to take over his role in your household, so what is he actually doing?

It sounds they need to sit down together and work it out properly, him expecting her to do all that is a piss take, has he looked at getting a cleaner or getting someone to sort meals, or transport, or any of the things his sister is doing single handedly? are you able to do a small part of it, like cooking some extra when you make meals to put in her freezer when he goes at the weekend etc?

I'd be pitching in if it was my MIL, I certainly wouldn't be saying it's not my job or my problem, but you shouldn't be having to do things that your DH could do himself.

I was the caregiver to both my parents at a younger age then most. It was a living hell. There is no way I would have expected a in law to take it on.

She’s very angry and sending me messages saying she will never speak to me again if I don’t “do my bit”.

Problem solved.

She is talking about expecting me to do things like taking MIL to appointments, cleaning her house, organising personal care, buying and preparing food for her

Are you able to do any of those things ?
I understand taking MIL to appointments might be tricky if you work full-time, but could DH organise with his sister a rota between them to do those ?
Cleaning the house, would MIL be accepting of a cleaner coming over once a week ? I can't imagine she makes much mess.
Organising personal care, as in you doing personal care or does SIL think you have more expertise in this area ? Word of mouth is useful for finding out the good care agencies.
Buying and preparing food. This might be difficult as MIL might not enjoy things she used to. Could DH have a chat with her about foods she might like now ? Is she able to put something in the microwave or does she need everything preparing for her now ? Is doing an online food shop something you could manage ? If you are looking at getting carers , twice a day would be good , the morning carer can prepare something to leave for lunch and the later one could prepare a meal for her.

I wonder if SIL is lashing out at you because she is hoping by doing so makes her Brother step up ?

Is this a cultural expectation?

Not your responsibility at all. If she needs something you could do and your husband and SIL aren’t available for some (legitimate) reason, it would be pretty awful of you to not to help at all. But no way should you be taking on the same responsibilities your husband should. If he can’t or won’t do it, that’s his problem to solve and accept the consequences it has on his relationship with his sister or his mother’s wellbeing

I think with regard to the children coming second to MIL, there are degrees of reasonableness. If MIL really needs a serious one off help, it would be unreasonable to refuse because you planned to do something easily rearranged with the kids. But likewise, MIL’s minor needs/wants don’t override the things that matter to the kids.

Of course MIL is not your responsibility. Support your DH by all means but your SIL is out of order. Is her husband helping MIL?

I'm not sure why it should matter to your SIL whether it's her brother or you who gives MIL care. Other than to ensure care is given. I would expect DH to do the DM caring bit and you hold the fort at home. I did the same when MIL was seriously unwell. I took complete responsibility for the family and he took responsibility for her care. We also came to see her as often as we could but he went regularly and reliably. When you have children you have caring responsibilities as well as elder caring responsibilities. How you divvy it up in your house is no concern of hers as long as MIL's needs are met.

Does SIL have children OP? And if so is she practicing what she's preaching to you?

Your SIL is way out of line but I’d try not to hold it against her long term, she’s probably in shock and grieving and it can send people loopy. Focus on your relationship with DH and supporting him to do as much for MIL as he feels he should.

Step right back, next time she texts send a simple message asking her to contact your DH to arrange stuff. If you want you can say to your DH if you and DSis can’t or won’t meet all your mum’s needs then they need to look at paid options.

How close are you to SIL? Would it be a disaster if you fell out? Or is this out of character as she is struggling with stress and grief?

If its a only a few months left then I'd help within the bounda of what I could manage. I'd take her to an appointment or cook her a meal where I could etc. I'd expect my kids to suck some stuff up (eg if they had to miss a couple of hobby groups because their dying granny needs something, I don't think it's a disaster).

If it started making me ill, or meant that I had to give less support to kids, or they had to start missing lots of things or important things, then no I wouldn't push myself.

I'd tell your sister in law that you won't hold her trying to force you to help beyond your capacity against her given she's going through an incredibly stressful time, explain that you and your husband are doing what you can, and any further discussions about your husbands share of care should go through him.

I doubt your mother in law (if she is a decent person) would want you to be burning out or neglecting your kids in the name of supporting her

Nope

YANBU and I suspect that deep down SIL knows this. She's upset, she's preparing for the death of her mother and is trying to find an outlet for her grief. It's not right now she's doing it, but I can understand it a little bit and try not to take it personally.

Sound like you are doing everything you can to support your DH and that he's doing all he can to support his mum, with in the constraints of your lives.

As this is likely to be a short term issue, I would be putting some things on the back burner (for all your sanity) but not everything. I'd also be doing my utmost to keep things as normal as possible for the children, who are likely to lose their grandmother soon.

That is an excellent question. How much is the son in law doing? Are they expected to do the same?

Tbf it doesn’t sound as though you’ll be missing much if she refuses to speak to you 😂

This is good wording.

Yes also make sure she has this detail.

This.

”Within the constraints of his own life” sounds like he’s not actually doing his fair share.

He needs to sort this, not you. Your only job is to help make space in his diary so he can be equally present. It’s his ex’s job to do that too. You shouldn’t be taking on loads of the step kid care.

Either just block her or reply “ I’m caring for both my own ailing parents” then block her
shes lashing out so keep it factual

you re the new member of the family so have become the scapegoat. A threat of not talking to you again because you wont meet her demands sounds like a good option

I assume her husband or partner is helping out too? Probably not. MIL isn’t your problem.

Absolutely this!

It’s a difficult and emotional time for all.

If your dh and sil haven’t the time or capacity to look after your mil, then you may need to escalate the care, and get in carers. It’s a big step to take, but sounds like it’s necessary. You can apply fur Attendance Allowance, which will help pay for this. There will be resistance but it’s often the best way.

Do not put your children’s lives on hold.

Your first responsibility is the children you chose to bring into the world. The second to look after yourself well enough so that you can do that to the best of your ability. The third is the children you chose to have as step-children by marrying their father. Your parents and DH are next. Then if you have resource, your MIL.

You can only do what you can do and your SIL is being manipulative and coercive. She is stressed and dealing with an emotive and complex situation so I can forgive that, but you shouldn’t be organised by it.

You and your DH should have equal
self care and leisure time and you both need to keep looking after yourselves so that you can parent.