AIW for being upset with my boyfriend's brother and his family?

I'm FTM (M now, using he/him), living in an accepting household with my mom (F38) and my stepdad (M39). Living the good life. I spend a lot of time with my best friend, who were gonna call Brian. Brian's awesome. He's been my friend since the summer, during marching band. Brian is two years older than me, living with his six siblings and mom. He has a brother (also FTM), who's my age. I start dating this brother, who we're gonna call Nick. Love him to pieces. Brian's Mom is homophobic and transphobic. She uses the wrong pronouns for me, but uses the correct name. She doesn't respect Brian or Nick for who they are. Up until yesterday, she had dealt with me being their friends, because I'm a good influence. Whatever whatever. I had been at their house often, helping with all the kids. Brian's Mom doesn't know I'm dating Nick, and I stay the night frequently. Yesterday, she was persistent about me being she/her. I found out later that Brian had let it slip that I'm dating Nick, and now I might not be allowed over, or to even see Nick. I'm upset with Brian and his mom. I'm losing my shit right now. Nick's worried that I may be overreacting, but this is a big deal to me. I haven't talked to Brian yet.

TL;DR, my boyfriend's homo/transphobic mom found out we're dating and I might be cooked. Advice?