You are quite early in the bonding process. Even though things were going well, it’s super important not to leave them unattended at this stage in the game. As you learned, things can change really quickly.
Bonding requires the bunnies to build trust between each other, and to decide who will be dominant. Only they can determine that, so your goal is to provide a safe space for them to do that. It is super important that you do not let them fight again, above all else.
As A&B suggested, a bit more pre-bonding and settling-in time might help.
Since un-met grooming requests are leading to scuffles, I would focus on preventing the fights from happening. When they ask to be groomed (by putting their heads down), pet them both to swap scents. They will both think they are being groomed and will have warm fuzzy feelings about the other bunny. This helps build a calm association and will soothe any hurt feelings over the fight.
Do check both bunnies really thoroughly for injuries. If you find any other more serious ones, I think it would be good to give them a couple weeks off to let them settle down.
It can be hard to not know how to procede (“Why can’t they just be friends!”), but it usually just takes time and a lot of patience. Since they fought seriously in one area, I would also not use that area again, as they can build a negative association to a specific place.
In addition to the petting technique, stressing can also really help. You can take them on a car ride together (have someone else drive, pop the buns in a bin, you sit in the backseat with them and prevent nipping). Bunnies crave comfort when they are afraid, so stressing can be a really useful tool to get past certain issues.
Overall though, 5 days in is really nothing, so more time is the best plan of attack. And do not let them fight again!
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.