oh, that would totally be louis being all "rose, if you don't shut up, i'm going to push you into the lake" but very gently while giving her a hug, LOL. louis isn't the most patient in any situation, but he's definitely more tolerant of his family members because he genuinely rather likes most of them
louis will be in 5th year so he'll be a year-ish younger than her, he'd definitely roll his eyes at her being protective over him but he wouldn't actually ever stop her either, because you know he soaks up all that attention!