Im going to be honest: It doesnt sound like they will bond. Youve prebonded for months and they still fought the moment they were allowed contact. You gave them months apart to ignore one another and they still fought the moment they were allowed contact. Youve tried stress bonding and they still fought.
The only thing that might help is to keep them out of complete contact with one another. One bunny in one room and the other bunny in another room. Keep them like this for three to six months (its usually two to six, but your bunnies still hold grudges at two months, so you need them apart much longer). Wash your hands inbetween handling. Dont allow them to see one another. Dont swap any of their items. Make them both feel like their completely single. After the three to six months, move them into the same room and prebond for two+ months again. If they still fight after this six to twelve month break, they will not bond.