It's pretty obvious what leads to most of their downfalls since they're not very subtle about it at all. As for the ones that didn't actively shit talk him like the singer, "five-san" is probably the mc since all their names are based on numbers and him being the 5th child. The youngest is hard...
She fucking announced that she was going to negotiate permission to use a beach resort with her boss and the black haired girl STILL goes "who knows" like a dumbass when the dude asked about it....