You can, but it’s awkward. We sleep on a removable platform with the bikes underneath. It’s a deliberately high platform, which isn’t ideal and is a bit claustrophobic, but we can get two bikes and full camping/holiday gear in there with us. Works for the odd night here and there (ie stopping on the way to the alps) but we’d not want to do more than that. I’m sure you could rig something better, but I use the van for work so I couldn’t get too fancy. One person and a bike is easy!
Lots of new Berlingos have a bench seat. As the seatbelt for the central seat is attached to the bulkhead behind the driver, you can’t remove that and still pass an MOT (passenger side comes out fine), so folding the driver’s seat down isn’t an option unless you get a two-seater. (This is all for 11 plate vans. May have changed.) My relatively short girlfriend fits behind the bullhead, I’ve no chance at six foot.