You can only do so much. It seems like you have done everything you can at this point. I understand your concern about having your cousins aware for their health but if you can't reach them, you know you have done your best to warn them.
It's time for you to focus on you and take good care of you. The added stress of worrying about your cousins is not going to help you. Hopefully your aunt will pass on the news.
Take good care of yourself.