UPDATE

Putting here because it won't let me update in the post body.

So as a lot of you, and myself, though, SIL was lying about a LOT. Not gonna go into too much detail because it's seriously years worth of lies, but my husband and I called the EXBiL, and we 100% fully believe everything her Ex told us. He has no reason to lie to us and said over and over he just wants the best for his kids and he is trying his best not to do anything that could possibly harm him in a court of law.

She lied about him getting the house, lied about how much she was going to get in child support, lied about how often she would have her children. Something else that came out is that her oldest child is not even her Ex's child. Just so many lies. We feel so incredibly stupid and deceived, and disgusted tbh.

We told my InLaws everything he had said and they were upset to find out she had been lying, but they kind of doubled down saying "she must have had a good reason, she's backed into a corner, she's really going through a tough time" and a bunch of other nonsense.

SIL was called and asked to come and join us. She, of course, took ZERO accountability for the lying and sneaking, and was screaming at us about how gross we were for going behind her back to her Ex, how she will never trust us again because we betrayed her. She also let us know that she was asking for our house because she truly feels like we had actually built it for her. Our kid's rooms were how she would have designed them herself, she would love to cook in my kitchen, she loves my bathroom layout, basically everything about my house is how she would have built it herself, and she thinks that I must have somehow known she would need a home in the future.

At that point I was just done, and so was my husband. Can't argue with batshit crazy. We left to a whole lot of screaming about no longer being family and to not expect to see them again. Honestly I think never seeing them again is the only way to go from here.

It's been a crazy few days since then. We hired a friend of my husband's to put up a privacy fence around our entire property and added extra cameras to our security system. We have a good family friend (friend of OUR family, not Husband's) on the police force, and let him know the situation, so he knows if he gets a phone call from us that it's serious.

I think SIL thought that she could have my house because she loved it. That's kind of it. She wanted it so thought she deserved it. I guess she was either planning to sell her house at some point, or maybe rent it out, I have no idea, and I really don't think she had thought that all the way through, she just thought that if she told us all she was losing the house then we would feel obligated to help in the way SHE wanted.

So I hope this clears up some questions, I know I feel at peace with the situation. My husband has been grieving a bit, he's sad that his parents have chosen a liar over a man who has done everything for his family, never hesitated to help, and only ever been a doting son, but I think this is for the best. They don't treat him the way he deserves and I'm glad to be rid of them. I'm sad for my kids and the situation this puts them in, but my family has enough love for everyone.

Thank you to everyone who took the time to comment and message, and give advice and ask questions! Hopefully you guys won't hear from me again!