I think it's obvious why they keep a little distance to Takebe. She seems like the fussy type who lectures them a lot.
As for not getting invited, she called it a "shotgun wedding" for a reason. It was sudden and not planned out. They aren't thinking ahead at all, just like she is, so of course they aren't more mature.
But they feel bad about worrying her or getting chewed out, so they focus more on themselves and family and don't report everything to her like they did as students.