Hi there, sorry you are having trouble with your boys.

How long ago were they neutered? It can take several weeks for hormones to drain. Even though they were together as babies, their smell changes a lot when they hit puberty, and again when they are neutered, so they probably smell very different to each other.

Have you done any pre-bonding cage swaps? That can help a lot. Basically swap who is in what cage every day or so, until you see a drop in territorial/aggressive behaviors (usually 1-4 weeks).

In cases where you’ve done pre-bonding, and they are still fighting in neutral territory, the next step is to try stressing. My first pair would fight on sight, and car rides were the only thing that got us past that stage. You’ll want to have a helper drive. You will site in the back seat, with oven mits or tennis shoes or work gloves on your hands. Have the car running, pop the bunnies in a plastic tub, and take them for a drive. Make sure they do not fight! You can pet them both and swap scents. It helps to have them site by side, heads facing the same direction, so they don’t start circling. I would go for about 10-15 minute drive if they are doing OK. Then put them straight back in their areas. Repeat the stress sessions daily for a few days in a row, and see if they seem to be going to each other for comfort. Of course make sure that they aren’t getting too stressed. Some bus can’t handle this tactic, so you might need to reassess.

Once you are ready for longer sessions, I would opt for as large a space as possible, in as neutral a space as you can find. A couple of pens set up in a garage or at a friend’s house can work great. Start them on opposite sides, and hopefully they will spend the first few minutes exploring. When they come together, be ready to pet them a LOT to calm them down. Keep petting and swap scents. Do NOT let them fight. Start of with short time goals (30 sec, 1 min, 3 min, etc), and always end on a positive note, even if it’s you petting them both.