I'm gonna say this has some nuance, and that the bigotry involved plays into people's obvious response to calling off the wedding a NTA move.

But the wording of the post makes me feel you would be overreacting. You're marrying this woman and not her family.

She want's her family at her wedding and she knows they're bigots and would like a stress free wedding. That doesn't make her a bigot.

Is it fair to ask your son not to bring a plus one and hide who he is on the day of his fathers wedding to make sure it goes smoothly, that depends...

How is it being asked and by who, if she would ask him herself and make sure he isnt hurt by it then that's fine.

It doesnt sound like she gave this to you as an ultimatum, or that she has any problems with your sons sexuality whatsoever.

It isn't nice to make your son have to pay the price of her family's bigotry when he and you are in the right here but obviously she's dreading her family's responses and it's a no win situation.

Shee is the one currently being selfish but ending it instead of working through this seems unreasonable.

So... sort of the asshole?