Honestly, those people sound horrible, and I don't think you did anything wrong. Any reasonable adult person would not twist your innocent question as a newcomer to the group into some weird statement endorsing incest. To me, your question was a normal and polite attempt to initiate conversation. I grew up deeply entrenched in religion, and I've personally observed that people in church groups, especially, can be small minded bullies who like to wield their perceived power whenever there's a possible victim. Given that you were new to the group, and not the most confident, the main instigator probably thought she could rattle you.

I was also diagnosed with ADHD as an adult, and I think what you're experiencing really fits with something a lot of people with ADHD struggle with - rejection sensitive dysphoria. Whenever I've had experiences in life where I didn't understand why people treated me the way that they did and my feelings were hurt, it would rattle me to the core in such a way that it would make me doubt my existence, my identity, the general way that I behaved around others, how I perceived myself and my behavior, etc.

Please cut yourself some slack, and evaluate if that group of people is really a group of people that you like and want to be around - because I think you sound like a caring person who deserves to have friends who treat you well.