Am I in the wrong?

My brother and sister in law are living in my parents' house and help pay the bills but other than that the mortgage is paid off. When I got pregnant I got kicked out of the house but now they're allowing me, my fiancé and my baby to rent the basement. My brother told me to call his wife and say thank you for letting us live there and that I'll stay in my lane and not interfere with anything...UM WHAT. I told him "I mean no disrespect but I should be thanking mom. I can however tell her thank you for giving up the basement and that we'll be there the whole time and out of her way." And he LOST IT. It's not even their house why am I thanking her??? And on top of that they got mad that I said I want downstairs to just be our space but they can come down if they need something in the furnace room. Like I'm going to be paying $800/mo which is MORE than half of the utilities and my family can't even have their own space?!! Now my mom is upset and wants me to apologize to him even though she knows he's in the wrong. He's 30 and throwing a fit over losing the basement when I'm about to lose a place to live in a few months unless we live there. I love my mom and want to ease her pain but I don't want to feed into my brother's ego. Am I wrong? 😩😩