Two can play the family guilt game. You are dealing with those who believe what they hear. “I can’t believe you’d ostracize me just because I can’t get the vaccine... what kind of family does that to their own flesh and blood?” Or... “ why are you always so controlling? I’m healthy, I’m not a threat to anyone, what gives you the right to tell me I can’t make my own choices about my body and my health?”

Or... Go around the control freak aunt, communicate directly with your cousin to assess her/his level of vaccine concern. None of your aunts business if your cousin wants to see you.