Likely all of the fights caused them to severe their bonds completely. Note that it is possible they no longer will be willing to bond together. There is one thing you can try before calling it quits, though. First thing first, until they are back to being perfectly bonded, youll want to keep them 100 percent apart. Different cages, different food and water bowls, different litter boxes, ect. You can keep them in the same room, but do not let them out at the same time together. Youll need to keep them like this for 2+ months; this also means stop with the bonding sessions (no excuses)
After those two months are up, start bonding them in a small neutral area. If they go right back to bad fighting, their bond cant be repaired. If they ignore one another or just nip but no fur pulling, its a good sign theyre willing to be bonded again. If they are willing to bond again, start super slow. 5 minute sessions, multiple times a day in the small neutral area. Do this until they stop nipping/mounting, then move to 10 minute sessions. After 10, do 20. Then 40, then an hour, ect. Dont be afraid to move back a step if you need to, and dont move to longer sessions until you feel they will be ok with it. As you increase time, you can also increase their bonding space