Wow. That has to hurt. At the end of the day, nobody (not even themselves) know how they would react to that until and if it happened.Dangit2019 said:They've gone to lengths to let me know that if I ever came out of the closet, they would absolutely disown me, and it makes me feel bad that they would say something like that so easily and still come back to assure me that they love me completely.
As for your question there has to be some similar circumstance, and argument with a similar form that when they say something against gays you could bring up about the other thing. "that's not what you said about X" so that the argument becomes about the fallacy via some other more neutral topic for them.
However, as they are deeply held beliefs I don't think it's likely they will change without consistent and strong evidence the contrary of whatever it is that they believe.