I am smiling right now, because this is familiar to me 😀 I got Thor first, then bonded Crysta to him. She destroyed my hay box (death by chewing), and the rug (shred-fest) but the payoff is that she defers to Thor and they get along. I don’t know if another female rabbit would’ve gotten along so well with my calm, but bossy boy.
Thor started to chew a fraction more after the bond, but we have a good relationship, to the point that when I say “No”, he stops chewing and I redirect him to something better. Have you considered that your boy might also pass on good traits to Belle? I say this because (while not the best example) Crysta copies Thor’s more confident behaviours, like pulling hay out with front paws, and throwing toys out of the way in one swift move, without walking around them like she used to. I also saw her try to lift a big tunnel out of her way, and this was not her behaviour when I first got her. It looks exactly like how Thor gets things done. Just a thought.
I think chronic chewers need dig boxes and secured/ heavy or weighted stuff to tear apart at (stuff that’s attached to something else so it doesn’t move). It may also be that Belle needs more exercise time (bar chewing). I’ve heard a few stories of rabbits preferring to do their business on soft blankets vs. litterboxes, so there may be a connection, I don’t know.
Thor also sat there when Crysta tried to hump him. He just ate his hay, and Crysta looked like she was climbing a mountain, haha. Maybe it’s a good thing that he doesn’t react, but I understand it is not your primary concern.
There’s no way to know for sure if your boy will be exactly like Belle. If Belle uses the litter box relatively well, and is a healthy little lass, those are two positives. There’s always a reason an animal does something, even if it’s just to be playful. If you figure out the “why” it may help you figure out a solution.