Having dinner with a homosexual couple?

My nephew is gay and he may be visiting near where I live with his boyfriend. They will not be staying with me, as I would not allow them to sleep in the same bed/room.

Is it affirming of their relationship to share a meal together? I tend to extend this to how I would handle other examples of inappropriate relationships in that I would certainly not participate in by ways of spending time with them as a couple (ie. a man cheating on his wife wanting to bring the other woman over). I am struggling how this would be done faithfully and in wisdom with them as a couple.