People enjoy things for entirely different reasons. One person might like to get tied up during sex because it makes them feel like they're being used or forced, while another person might like getting tied up during sex because otherwise they can't help pushing their partner's mouth/hand away during stimulation because it's so intense and they really want to ride the feelings all the way through to the end. Similar from the outside, completely different on the inside.
Similarly, some men might like to see their wife with another man because it makes them feel inferior and humiliated, others (like you!) might like it because they enjoy the "sexual compersion" of seeing their wife's pleasure from a third-person perspective.
Just because your situation looks outwardly like the "Hot Wife" scenario doesn't mean it has anything at all to do with that, so don't let it bother you! Enjoy it all you like for the reasons YOU like it. Or if, as others have said and as you fear, it might be inching towards an uncomfortable place, then by all means let them know that you want to give them a little space. If they care about you, which they certainly seem to, they'll understand and figure out how to make it work. But if you do that, do it because it's right for you, not because other people's humiliation fantasies bear an outward similarity to something you enjoy for different reasons!
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.