Marek made a face back, scrunching up his nose, and followed, refusing to be left very far behind. He was used to his genial questions going unanswered, but he never gave up, regardless. He didn't keep up a steady chatter, as tempting as that was, because his grandfather would know it was purposefully to annoy him. That wasn't really what he was trying to do; he was simply treating his grandfather as if he really were the kind of grandfather Marek would want, friendly and caring about what was going on in their lives. Maybe eventually it would be returned, though that was doubtful.
He had a pleasant enough smile on his face as he took his seat next to Melinda, since he hadn't been directed to sit anywhere else. So far as he was concerned, if he wasn't given direct orders, he would do precisely what he wanted to do in this situation - which was to support his sister. "Thanks for letting me stay," he said, folding his hands in his lap as he sat up straight.