How do you think the boys would react to their s/o wanting to be in a poly relationship with two of them? Do you think they'd be willing to share like that?
Hm...some of them would, but I honestly think some of them wouldn't!
(Sorry if these aren't quite the answers you're looking for, but I'm trying to be truthful to their characters as I understand them.)
Nathan would not be willing to share his partner with others. I think Nathan was raised in a very traditional home and wouldn't really enjoy the thought of a partner who isn't monogamous, even if he's aware of it going on and is able to participate. If his relationship with Trindle was any indication, Nathan likes all of his partner's romantic/sexual focus to be on him, and I think he'd start feeling insecure and sad if his partner focused that on someone else.
Pickles on the other hand would be very cool with it. I think he enjoys being monogamous with certain partners who want that, but he's totally up for a relationship involving multiple people if everyone's on board and having fun (because that's what Pickles is all about, right? having fun!).
Skwisgaar actually prefers poly relationships, so his partner's in luck. They take some of the pressure off of him. He's really great in the bedroom, but I have a feeling that when it comes to actually being in a relationship, he can be sort of lost and unsure of what to do (he didn't exactly have the best role model in that department). So being in a relationship with multiple people ensures that the pressure of conversation or entertainment isn't squarely on his shoulders.
Toki's fine with hooking up with lots of groupies just for casual sex, but I think his romantic relationships outside of that are strictly monogamous, so that's a no-go. If he has a partner that's his partner, no one else's, and he can get really protective of them, if not a bit territorial.
Murderface is just fine with it. Multiple people want to be in a relationship with him?? He'll take it! He'd be a very exciteable and willing partner, always going out of his way to make them happy so they stick around. He can get a little nervous about it sometimes (more partners means more of a chance to mess things up) but some physical affection usually makes him feel more secure.
Charles likes the idea of a poly relationship. He's a very busy man. He knows realistically there's not much of him left at the end of the day to completely satisfy his partner, so he knows it's probably best if his partner could rely on someone else for their needs, too. But in practice? I don't think he'd enjoy it. I think it would make him feel useless and unnecessary.
Magnus strikes me as the type who would say yes when he really means no. He doesn't want to share his partner at all, but he doesn't want to lose them either, and he thinks they might leave if he isn't willing to do this. So he puts on a brave face for a while, and for the most part he seems totally chill with it, but eventually his jealousy and insecurity would eat him alive, and the relationship would dissolve, and he'd be left alone. (Unfortunately, his monogamous relationships all tend to end the same way...)