I would say something because it is clearly making other family members uncomfortable, and it is possible that they do not want to say something because they do not want to feel like they are the ones ruining the fun. Doing so may also make the family members who are uncomfortable, gain more courage to speak out when they are uncomfortable about homophobic jokes or similar situations. I would also stop them as letting them tell those jokes might make my cousins who are telling them come off as homophobic, even if that is not their intention. Some people might also take the jokes seriously and become more bias toward gay people as a result, so that is another reason I would stop
I would say something because it is clearly making other family members uncomfortable, and it is possible that they do not want to say something because they do not want to feel like they are the ones ruining the fun. Doing so may also make the family members who are uncomfortable, gain more courage to speak out when they are uncomfortable about homophobic jokes or similar situations. I would also stop them as letting them tell those jokes might make my cousins who are telling them come off as homophobic, even if that is not their intention. Some people might also take the jokes seriously and become more bias toward gay people as a result, so that is another reason I would stop