Alyssa,
Have you thought, and I know it sounds crazy, but biting their ear when they nip/bite, then tell them "No Biting". When the "OUCH" didn't work or the squeal I just picked them up, bit their ear, NOT HARD, but enough that they felt it, then I would say "NO BITE", we give love, kisses, and snuggles here. Then I would pet them, kiss, and snuggle until they were clam and/or chomping...most of the time they would put their head under mine after the bite (that I did) and want snuggles/forgiveness. But I think this will teach them you are "BOSS BUN". This should help some so you can save your fingers/hands because they will learn NO BITE means something or BE NICE, this is what I tell my buns. 90% stops them in their tracks, sometimes I need to say it twice, and I currently have 28 rabbits.
I know many will not approve of this method - but you HAVE TO BE CONSISTENT, for this to work. EVERY BITE/NIP you would need to do this. It's is time consuming, but it works and it might help them to stop nipping each other. I have rabbits who will occasionally nip that are in pairs and 2 warrens/herds. They will occasionally have a tussle between them when I begin to hear the "racing" I will tell them STOP, BE NICE! Typically ends the tussle/chase. My biggest issue is they pee/spray each other still to show dominance, it seems like, there is one male and one female in one of my warrens/herds that do this mostly. The rest will chin their sibling/mom. (They are all fixed BTW).
Some stress bonding might also work...I know you didn't want to do that, but it might be where to go from here. A little stress make the heart fonder??