Will we ever get our house back

I’d expect she will be there for a year or so tbh

I can't believe you and your DH kicked one of your kids out of their bedrooms for an unknown amount of time to accommodate this batshit behaviour.

MIL needs to go. Either to a rental or a hotel. Now.

DH should be as concerned about the disruption, kids sharing, excess storage stuff as you are. Is he not?

Sorry that your are going through this nightmare. I could barely last a night with mine before I’d choose to live in a tent instead.

A frank conversation and the suggestion of helping her find an interim rental may suddenly speed up her departure.

Takes months and months to buy a house and that's when she finds one.. perhaps you shouldn't have agreed to this OP. Nice to be nice but...!

What happened during the house sale? Was the idea that she could sell chain free proposed then? I wonder if she has treated her house sale and new purchase as 2 entirely separate things. She sold, moved in with you, but has procrastinated about the purchase, believing she had all the time in the world. You saw it as very temporary, she viewed it as an open ended offer that meant she'd not have to rush and only buy when the perfect, Goldilocks house came onto the market.

I'd be sending her links to houses that meet her basic criteria on a daily basis. It may require you to be the driving force in the search. Also send her and discuss storage options. For someone's entire house to be inside yours for this long is very cheeky IMO. She must know her grandkids have sacrificed their separate bedrooms to accommodate her. Time's up and she needs to find somewhere. Market isn't brilliant for volume of houses but she's in a very strong bargaining position now.

Perhaps put it to your husband that you wouldn't want any resentment to grow if she stayed too long. Definitely things in storage is reasonable, more than reasonable, her renting a one bedroom flat would also be reasonable. Staying whilst awaiting completion is probably most people's comfort level, the situation you have is more than generous and would test most relationships. I love my parents but I would be testing our relationship to have them move in or me in their house. It's natural to want your own space. She might be happier if she rents for a while. Good luck

Also your husband can get stressed etc, that's okay, he needs to think about all his relationships, his marriage and the needs of his children, not just his mother. He can feel uncomfortable and he can talk to her.

is she actively looking? I’d be bothered if she wasn’t actively looking and going for viewings. Getting her stuff moved to a storage unit is definitely the way to go. How is she otherwise? Helpful? Considerate?

@Temporarilypermanently You could always start having very loud sex - perhaps on those occasions your DCs are out but your MIL is in. 😈

It is a bad idea to let someone move in for an unspecified period, hopefully you'll be more careful next time! But you can explain to MIL now that you haven't the space for a long term stay and she needs to move out in (say) another 6 weeks at the most, into a rental if she isn't ready to move permanently. Perfectly reasonable to say that.

She's moved in with you on the sly.

Does your DH actually want her to move out?

It's been 12 months and 6 weeks. [I'm hearing Sinead O'Connor in my head right now] but realistically inflation is going to erode the value of her money long term.
She is presumably retired and could be out house-hunting every day. The market is super quiet and it's a good time to get better value and she's a cash buyer. Your kids can't share indefinitely and your home isn't a storage facility.
So practically speaking, I'd be proactively booking appointments for the three of you to view everything within a 15 mile radius every Saturday for weeks ahead.

I would look at bills though and whether an extra person is impacting this e.g. if you and DH work all day and kids are at school, is she watching TV and using more electricity?
Is she contributing to food as I assume she is eating with you, so with an extra person that might also be a bit extra?

It's definitely a concern if she hasn't found a property that she likes more than 12 months after putting her property for sale. Is she actively viewing properties?

Are you worried that her plan was actually to move in with you permanently? Will your DH get offended if you raise this with him and accuse you of not making his mother welcome?

What is she like as a guest? Is she low-maintenance and helpful or high maintenance and difficult?

Absolutely. You need to have a conversation with your Dh today. I think she is moving in by stealth. DH snd I are already discussing how we will manage the situation if MIL is widowed.

I’d ask her to look for a house to buy or rent as it’s time to move out soon. Look at storage lock ups and move her stuff out asap to give yourselves some room.

What age are your children? I agree there needs to be a deadline here. If you don’t want her living with you for the love of god don’t do the annexe thing!!

Push the fact that the children need their own bedrooms back and give a deadline. Offer to help find a rental property for the meantime, that may speed her up. Your DH feelings don’t trump yours and your kids.

Don't even mention the word Annex

It's a trap...

I wouldn’t build an annex. Just think about it : long hassle of building works and then she still will be in your house daily a lot.
I would think what you could tolerate, work out a realistic plan of encouragement ( putting things into storage, etc) and then I would the give her date for going into rental. A date for moving out to a new bought house would be too far away so rental it should be.

Neither my mum nor my MIL is welcomed to live in our small house for long term and I don’t think it’s mean on my side - I’m just being realistic. I’m sure my DH share my views.
My MIL was in this exact situation with her daughter. Only they were doing building works in their new house really slow. She said that they need to move out - it would speed up works. SIL was very upset for some times, but surprise, surprise- the building works went much quicker when they moved out. After a year no one remembered the disagreement.

Bloody hell, don't build an annexe! She'll be permanent!

How old are your Dc?

I would not be having them share a room during exam years.

Even if she finds a property tomorrow it will be a minimum of 3 months and if her vendors need to find somewhere, it could easily be 6months or more.

Does she really want her staying permanently though?
I am wondering if this is what MIL was possibly aiming for.
Is MIL paying anything towards staying?
I think if you are going to go down this route you need to be careful. Someone I worked with sold her house along with her dad and they all moved in together, but with the sale of both homes they purchased a large three storey home so that they could have their own space with the provision of being able to rearrange things as the dad got older and in need of more help, while the children would be able to have the top floor as they became more independent and older.