Hi there,
Hmm, the charging with the tail up sounds more like a dominance display.
If the basement is connected to their hutches, and they have access to their hutches, then it’s definitely NOT neutral. Semi neutral at best, but if they can go in and out of their hutches that makes is not neutral for sure.
In general the one grooming is the submissive one, the one being groomed is dominant. In bonded pairs both with usually groom each other, but in the bonding process grooming the other rabbit a way of saying “OK you’re the boss”. It’s so hard to predict who is going to be dominant, so don’t worry if they don’t meet your expectations. And honestly in many pairs its really hard to tell who is boss bun.
From what you describe, I think you should try for some long sessions, but in true neutral space. I think they are doing well given the space they are in isn’t neutral, but it could be contributing to the chasing and charging that is happening. Although with the binkying it might all be fine? It’s hard to know without seeing it….
If you could set up a pen in a room they’ve never been in, spend several hours there and see how they do. Then the idea is to work up to long sessions (8 hours), and eventually you can try them overnight in that neutral space (supervised).
If you have several days where you can supervise non-stop, you can also try marathoning them, which means starting them together in neutral, and not separating them again, but supervising until they seem bonded in neutral, then moving to semi neutral (continuing to supervise), and then finally to their final home (and then supervising again until you are certain they are solidly bonded). Given that yours are doing well in the space you have, they might be a good candidate for this (assuming you have the time to supervise for several days!).
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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.