imho Chihiro' s innocent. Sure, he could've told Madoka earlier that grandma's coming, but its not like that would solve the whole baggage between Madoka and granny. And even if he's very mature for his age, Chihiro still a kid.
On the other hand, neither granny and Madoka tell him anything about the family. Chihiro picked up on cues that Madoka didnt like granny, but when he met her, she's actually a pleasant but kinda eccentric person, well at least in front him. So, can you fault him want to know her better?
But we know from Madoka's monologue that granny is actually a neglectful (and kinda toxic?) parent, and that there's an element of regret in the interaction between grandma and Chihiro. After all, dont forget that Chihiro's mum DIED of overwork on the very first chapter and nobody helped her even though she came from a very wealthy family.
Anyway, Chihiro's a cutie, Madoka and granny are awkward as fuck, and the Hinos are practically a really good people and a really good family that tries to help Chihiro when her mom died and tries to help Madoka raises Chihiro even when he's awkward af and cant go interact with people for more that a few a hours at time