Chrollo isn’t very likely to go out of his way and assure them, honestly none of the adult trio really are. They’re just not like that? It’s only if Chrollo could see that it was really bothering his s/o that he would address it, but in a frustrated manner because they were keeping it from him rather than telling him straight up. He doesn’t like meandering around the point. And a self conscious s/o might not do well with him because of that. If they have a problem, they need to address it themselves, and he’ll only want to talk about it once or twice before he just doesn’t know what else to say that will soothe them. He also might forget that they’re self conscious? Like he’d introduce them into situations, maybe public and crowded situations, forgetting that they might not like it because they’re self conscious. He actually might be willing to pull them aside or get them out of there, but a majority of the time, he’ll just hope they endure it. Really doesn’t have a sensitivity chip to deal with those sort of things

Illumi is the same way, but mostly because he just doesn’t know how to reassure them. He’s blunt and lacking the sentiment needed to really comfort a self conscious s/o. He’d probably be the one to try though, but in a very nonsensical, irregular way. Would probably go into some biological talk about different body types and what not, but would also be the dude to suggest resorting to a diet or working out. Like Illumi just doesn’t have tact, and doesn’t understand that it might be offensive. If his s/o told him it was offensive and insensitive though, he might take that to mind and not mention it again 

Hisoka doesn’t really pay much attention to it? The fact they’re chubby is evident, but it’s not a big deal. If they were his s/o then it’s obviously for a reason, because he doesn’t just go around accepting people with open arms. So for someone as particular as Hisoka, if he doesn’t pay attention to it, he just expects his s/o not to either. He’s awful at consoling so if they ever expressed their insecurities, he just wouldn’t know what to do