Neutering lessens such behavior, but it doesn’t guarantee that a bun will never mark or fight. Block off the lounge so they can’t jump up on it, since it smells a lot like you they’ll want to mark it, it’s common for bunnies to mark such things (couches, beds, etc anywhere human scent is strong). You can use NIC panels to block it off, or place cardboard boxes up there so they can’t jump up when the buns are out.

My rabbits are different in sizes and they don’t fight. It sounds like it probably is the food, how many food bowls do you have for them?

I was under the impression bonded bunnies wont fight, hopefully someone will chime in but you may have to rebond them or separate them.

Neutering doesn’t always give bunnies perfect litter habits. My girl has been known to mark territory from time to time and she’s been spayed for years. It is worse in new places and was the worst when she was first bonded to Otto.

As for fighting – is it really fighting? Or just some chasing and fur pulling? Hannah will chase Otto and pull some fur out of his bum, or just “goose” him on the bum with a little nip. They don’t fight and Otto has gotten used to it, but early in their bond it did cause some tense moments when Otto decided he’d had enough – even then they didn’t really fight, but they were circling and getting angry with each other. All of this is very normal behavior, but if it’s actual fighting it might be that their bond isn’t as secure anymore – are there any new pets, people, or changes to their routine? How long have they been bonded? Size doesn’t matter in a bond – just personality.