As far as I can figure out, they're disagreeable because they're Robespierristes; Mantel wants to like Maxime even though she's a Dantoniste, so anything he does that doesn't conform with Dantoniste ideas, she has to blame on someone else. And who would she find it easier to blame than his adopted family and his closest friends?

XD Vaguely appreciate indeed! In all seriousness, though, I don't really have a good theory on this one... Because Danton and Desmoulins also have terrible relationships with their wives. (Well, Danton more than Desmoulins, since, while Camille has a pretty cruel sense of humor in this, Lucile seems to have that in common with him. >__>)