Hmmm ok – and is there a reason you are wanting a use a new neutral territory – as apposed to the one you were already using that was mostly working? Or at least working a lot better then the spare bedroom.
Once they have settled down – while still swapping their stuff / cages (I still do that even while bonding) – I would try them back in the other neutral area you had been using.
I found my bunnies weren’t big fans of change.
I also found that the big break through happened when I was able to do a very long session – the first time I was able to do 5 hours – As mine were the same with both wanting be top bun with Rupert especially being demanding for grooms.
It was like after hour 4 they were kind of like … “Ok this other bunny isn’t going anywhere…..”
I also did lots of petting them using the same hand to blend their scents and found when I stopped one would usually start grooming the other.
Again, I’m no expert – just what I found with my two dominant bunnies.