Hi, I hope this still helps.
I have four buns so I’m trying to bond all four but man its a job haha. My two buns had love at first sight but I know that when you are bonding or rebonding, you need to bond in a neutral territory where no other bun has been before such as a bathroom or kitchen.
I would keep their pens separated by a couple of inches and do not let them have play time in the same area, it will only encourage territorial behavior and fighting.
After you do that, I would start in the bathtub and have gloves handy to pick one up if they start fighting. Stress bonding such as car rides always help the process more faster. Start out doing small times together then do longer sessions. As they do better then you can move their houses closer together.
Also, I am trying this right now, have two stuffed animals “stunt doubles” and have each one mark their scent on one. Then switch the bears and once they see when they fight the bear the bear doesn’t react, they will be comfortable and when you introduce them face to face, they shouldn’t fight. It all takes time but I hope this helps!