My honest advice is to prepare yourself to live without them. Imagine telling them that you don't have to ever see them again and that you'll not accept any harassment from them. It's not because you'll need to have that conversion though, you probably won't need to. You just need to get yourself ready for whatever the conversation is going to be. Once you're ready for whatever happens; try to have the best version of the conversation and make them understand that transition is just something you need to do. In my experience, many people that have backwards thinking feel something like "[whatever group] are terrible, dishonest and gross! Except for [relative or friend] he/she/xe is one of the good ones!" I still hate that they're that way, but it's better than dehumanizing their dearest loved ones, most people won't do that.
Good luck with it! If you feel it's a conversation you're about to have, just be honest, lay it out plainly, and hope for the best.
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