I assume side fridge kid is the little brother (honestly he might just look older than the Duke since he's always sort of chibified).

I wonder what he's going to be like, it seems his sister is the rare family member who hasn't shunned him so God knows what the replacement heir will treat him like.

Can only assume he's been doted on and the like since the Duke has probably not been on the cards to be heir for quite some time. Poor Duke, imagining what he'd be like if he didn't have Rob and Alice breaks my heart.