I’ve currently got a recently bonded pair and a single bun, who I think is sister to the bonded girl. Its clear that bonding them as a trio is going to be a long tricky bond. Gina is in a 4’x2’x2′ size bought cage, it is way too small for her to live any amount of time in (I caught the two girls running wild and any cage was better than none). The bonded pair had over 90% of the dining area til yesterday, when I added a run to Gina’s cage, giving her quite a bit more space, and them less. The dining room is around 100 square feet, so they still have plenty of space left, esp given everybunny gets floor time twice a day, when they can use the living room, stairs and landing.
This did however leave Jenny, the bonded girl, so cross, she refused to speak to me until the next day, and was still annoyed for most of the second day.
So yes, a big enough space can be divided, and yes, you can expect the current owner of the space to be pretty annoyed with you.
There is another consideration, and that is will the buns be able to bite each other through the xpen walls? One reason Gina had to be kept in the cage for the first few weeks we had her, is that she tried to bite and claw everybunny else. She has now calmed down to just hair trimming nips, which is why I’ve been able to add the run to her cage. The run bars are wider spaced than the cage bars, and if I’d added it a week ago, there could well have been blood drawn, making a successful bonding between the trio harder to impossible.