Yup, your sil is pond scum. She reminds me of my brother who tried to throw my mom out to the curb because he got tired of her living in his underwater condo with her paying half of his mortgage because they didn’t want a stranger to pay full rental price. That’s what he did to her for her helping him out when he couldn’t sell it or afford two mortgages.
They were trying to avoid a short sale. It still happened. It’s a good idea to not buy a house before you sell the one you’re living in. Don’t assume you can rent it out and don’t harass a family member to buy it from you. Why should they be left holding the bag of your mistake.

Needless to say, I called him out on it and we had a fall out. I haven’t talked to him in 2.5 years. He just now started fessing up that it’s his fault and that he lied about some of the stuff that happened.

Greed does horrible things. I lost a brother due to his greed and envy.

I don’t want to have to deal with someone like that.