Thanks for rescuing Oreo! It sounds like she doesn’t like being put in her hutch, which is understandable, but still annoying! How big is the hutch? When she bites, give a high pitched squeal so she knows it hurt you. You can also try associating the hutch with something positive – I always give my bunnies their veg portion when they go back in after running around – in fact, I just need to put their veg in, and they go running in by themselves.
Have you changed anything about Spot’s litter box? Can you move it to the spot where he’s peeing? it is strange that it started before Oreo, as my initial thought was that its a territorial thing.
I know you didn’t ask for advice on bonding, but most people here would advise not bonding until both rabbits are spayed or neutered – as you’ve seen yourself, unspayed rabbits can be quite unpredictable and aggressive, and if she turned on Spot, it could end in a fight that would make the eventual bonding harder.