My step son can't come to bbq

My step son is 15 almost 16. I've been in his life since he was 3. He was my first baby l. I've had two kids with my husband. 3 and 2 months. My mom is having a bbq and we were all planning to go. My mom called me and asked if I could just bring family to the bbq. I said none of us where bringing friends and she said "No. I mean FAMILY! Like you, Rick, and my granddaughters." I asked why we wouldn't bring my step son and she said everyone loves him but she really just wants real family. I said he is real family and she said he doesn't hug them and he doesn't even make eye contact with them. My step son is REALLY bad at eye contact. He's always looking at the group and really doesn't like being touched. I told her him not liking those things doesn't mean he's not family but she kept saying it's one event without him and it shouldn't be a big deal and most teenagers like staying home by themselves. I said if he can't go than we can't go and I will never make him feel like he's not family. My mom said he's our family not there family. I said if my family isn't there family than I don't want to be family anymore 🤷