Bridesmaids Luncheon

So I am trying to figured out who gets invited to the bridesmaid Luncheon. My mom is hosting it for my bridesmaid’s ! So i am inviting my 9 bridesmaids, my mother and my fiancé’s mother. He doesn’t care if his step mom is invited. So it’s up to me to decided if I want to invite her. She hasn’t done much for me. We rarely see his dad and his step mom. His mother has actually done stuff for us as a couple and actually made an effort with me and with him. So that is why I would rather not invite his step mother to the bridesmaid luncheon. Since His half sister & step sister in law are not bridesmaids. Only his full sister is. So it’s like I don’t invite all three of them or I have to invite all three of them. Just to be clear, his step mom, half sister and step sister aren’t getting ready with mom on the day of. Only his mom, my mom, the bridesmaids and my grandmas. Please let me know your thoughts but be nice please. I am super stressed about the entire thing. I don’t take constructive criticism well right now.