I think you need to go back to basics with them – take out everything absorbent, including hay, and clean up any and all pee accidents as soon as possible. Also, I could consider adding another litter box if you only have one – they might just want to be able to each have one, in case one is occupied.

Are they peeing in large puddles? Or just small spots? When my bonded pair first moved in together, I found that Hannah marked a bit for a week or two – she would just leave small pee spots around, not large puddles. If they’re leaving small puddles I think it’s probably marking and you can expect a reduction as they get used to their new space and you keep it clean. If it’s large puddles, it’s more of an issue with deciding to not use their litter box for the majority of their peeing.

eta: I just re-read my post and noticed I said to take out hay – I meant to clean up the hay so they can’t pee on it and just put it in the litter box. I wouldn’t want someone else to read this and think they should get rid of hay! I just know my bunnies will throw hay all over the floor and then pee on it if I don’t clean it up fast enough.

Change confuses rabbits and it can temporarily throw out their litter habits. I agree with Elrohwen above, especially about adding another litterbox. be diligent in cleaning and give it a week.