Awkward. I can understand why your wife is still friendly towards them, even if she isn't into that kind of kink anymore. And I can totally understand why you don't care to meet them. It's healthy to acknowledge that your wife had a past and that's it all in the past, but you shouldn't be forced to deal with it in the present tense. And as your wife, it would be nice if she displayed some concern and consideration for your feelings about an awkward situation. But she's more focused on her own feelings. Given the situation, I don't think it would unfair for you to try for some kind of compromise. Is this going to be a short visit? Are they planning to stay at your house? Though uncomfortable, it would probably be better if they stayed at your house, so that nobody involved got the idea that there might be another threesome during their stay. If they stay at a hotel and you avoid them, that could leave you feeling anxious when your wife is visiting them at the hotel.
Good decisions come from experience. Experience comes from bad decisions.