I'd also say it looks a bit big for bonding.
Also, are the wooden things brand new? And the tube? The tube looks nibbled. If it was in with any bun before, it will be 'theirs'. By neutral territory it means EVERYTHING has to be neutral. No toys that would have been in with either of them.
I'd be worried about the levels and the hidey places. It'd be easy for one bun to spook another who was asleep, which could lead to a fight.
IMO, remove all the boxes, tubes and wooden things. More hay and a smaller space. Feed food periodically throughout the day.
P.S you don't seem to have a litter tray? Get a large one and put the hay in there. They'll eat together there and pee/poo together there. Using a litter tray should help stop them using different corners as toilets. You want them to be using the same area for a toilet.