AITA for not agreeing to co-sign mortgage for in-laws?

Long story short, my wife is pushing me to co-sign a mortgage of $600k for my in-laws. They won't get a mortgage on their own. My brother-in-law already refused, but my wife isn't ready to listen and keeps saying her parents are gonna pay the mortgage on time. She is saying I do not trust her and her family and should do it without any hesitation as we are a family. She stopped working by choice after our marriage because I make a good living but am not super rich, honestly. I am not willing to do it at any cost. She doesn't know how hard I work to make money, and I don't want to end up paying their mortgage if they fail to do it. Am I overreacting? What would have you done if you were me? How would you handle the situation?