I would also encourage bonding AFTER they are spayed as the dominance and territorial issues driven by hormones my be challenging to overcome.
But if you decide to try this anyway, or just do this after the spays then here are my tips for the mounting situations.
Normally during bonding, it’s okay to let the dominant bunny mount for a little bit. However, if it’s on a constant bases then the passive bunny will need a break, as this can cause fights or cause too much stress for the passive bunny – to the point where the “stressed” bunny stops eating or deals with a gi slow-down.
Also, if the passive bunny allows mounting at all, then comforting, like you are doing is good. Just don’t let the mounting go on and on and on. After a 20 seconds or so just gently push the dominant bunny aside for a couple of minutes. Eventually the dominant bunny should feel satisfied with getter her point across. The mounting should start to subside (for some pairs it can stop after a few days, but the average is a few weeks – but this is also based on bunnies that are fixed)
I’m glad that the white bunny isn’t screaming anymore. If it happens again, I would just double check that the white bunny, being new, doesn’t have any physical issues that may cause pain when being mounted. (some bunnies do just scream when their are scared, not physicall hurt, but I would do a body check to make sure there isn’t any place on the white bunny that may seem more tender than normal)
Keep us updated on what you decide to do.