The same way you would bond two bunnies
Dont try to bond them before they are all neutered, spayed, and healed. While you wait, can you keep their cages close, not but close enough to fight? Put the fixed bun’s cage in the middle so that the two unfixed buns dont breed through the bars. Keeping them this way allows them to see one another and smell one another in spaces they feel are their territory. It helps them get used to having one another around in a semi close area, without them being close enough to fight about it. Keep switching the towel pieces around while you do this too, so they can learn it is safe to have the other bunnies actually in their territory
After the two months (the waiting a month for your bun, and waiting a second month to heal), put them all in a box together or take them into the the bath tub. Start with a ton of short (5 minute) sessions per day, and slowly increase the time they are in there together every. For example, you can do about 10 5 minute sessions on day one, then on day two try 8 or 9 15 minute sessions, on day three do 7 or 8 30 minute sessions, ect. Nipping is fine, but biting, latching on, and fur pulling is not acceptable. Mounting is fine for a few seconds, so pick up the top bun if it lasts more than 10 seconds or if the bottom bun looks too stressed out. Give everyone lots of pets often. Stop circling when you see it start. Ignoring one another is a good sign, but try to get them to interact if they ignore too often, maybe add some hay or greens. If you have to separate them due to fighting/scuffles, put all three of them next to one another and pet them for a good 30 seconds+ then put them all back into their cages. This is so they end every session on a friendly note, even if they tried to fight