Hi!
It sounds like you’re moving pretty quickly. Normally, we recommend at least a month of prebonding, which is swapping them between cages, not just having them side by side. Swapping is very important because it means they lose track of what territory is ‘theirs’ and also get used to the smell of the strange bunny. Finn is probably attacking because he feels territorial, if they’ve already been in all the space in the house.
I would go back and do at least another month of prebonding, then find somewhere completely neutral to start your bonding. This could be a friends house, the car, a bit of fenced off garden if you have one (outside doesn’t retain territorial marking smells so easily as indoors), or a neutralised space like a pop up pen (cheap on amazon) or an xpen if you already have one with the walls and floor covered with clean blankets/puppy pads.
I can’t emphasise enough the importance of enough prebonding, and neutral space
they’ll be like different bunnies!
Can I ask how long they’ve been spayed and neutered for?