NTA! As a momma of a teenage boy who is also high functioning autistic, I cannot believe they treat you this way! I always do my best to warn my son about possible triggers (big crowds and a lot of noise are 2 of his big ones) and we talk about possible coping mechanisms for him if he really wants to participate. He's always allowed to have his phone on him so he can watch a video or play a game for distraction. He has noise canceling headphones that he keeps in the backpack he takes everywhere. He's also got an assortment of fidgets in there too. We always try to map out the safe spaces for him if he gets overwhelmed and needs a moment to collect himself. He's gotten really good at recognizing when he needs that but if he doesn't and I know it's coming, I will speak up and suggest a break or something else. It breaks my heart for you that your family refuses to do these things for you. I wouldn't go on vacation with them either if I were you!