Among other things, you are there to ensure the heterosexuality of the event for them, so they can explore each other a little bit without fear of commiting. They sound like trad guys and trad guys are raised to think that sexual identity is all or nothing and that if they let in even a little bit of gay their entire identity will shatter. It’s sad that the culture does this to them - they do it to each other, really. Have patience. Let them go at their own pace. Exactly as you would with any partner, with any sexual experience.