I think the author is alluding to the idea that the grandfather knows something that we don't, like Daisy was saying something about how it feels like he knows the future from how he talks. So I'd have to assume that maybe he can't kick out the two shitheads on his own without consequences or the family falling or something like that
Cuz no yeah, he's very frustrating as a character and I really hate him but I'm trying to give the author the benefit of the doubt ig
Or maybe he's just written this way to strike a nerve with people who had a similarly frustrating patriarchal figure in their life that they could never please but if they fail to tie it in properly to his character, it'd be bad writing imo
I'm pretty sure what the author's going for with the grandfather's character is that he's suppose to be your typical patriarchal figure who's strict but fair and cares about his family very much in a traditional sort of way. The problem is that the grandfather's reacting to the family drama as if he has no idea what the hell the shit-duo has been up to despite the fact that it's practically public knowledge at this point that they're horrible people. So it comes across as either no one tells him anything and he's incapable of reading the room, or he's way too forgiving to the point of being delusional, or he's biased AF for shit-bro. None of those options make him a likable character.