Your father is only doing this to hurt you mother further, in my opinion. Of course I think it's also only because he has been hurt himself and wants to hurt back. It's a Catch 22 thing. But, in either case, he really has no use for the bike, but he'll keep it just because it's hurting your mother. If it were me I would have no qualms about taking the bike myself and just giving it to your mother because it was and is her bike as it is not part of the actual house itself.