Connor is, I think, only selling books to make room for more books. Or these are ones they've accidentally got two copies of. You should see their library at home. Always has his nose stuck in a book when he's bored.
He's Mags's cousin, and Ali's... Well, apparently they're not dating, but they're certainly not purely platonic. Why else d'you think they get stall tables right next to each other?
Everyone here knows them. They've been working for Darroch since they were 18, and do freelance work across Scotland. You'd think he'd be sick of seeing everyone by now. Maybe they're selling here for another reason.