my only thought is that since she was left with one ovary, she’s still getting hormonal rushes from it and perhaps having new people around made them feel nervous and triggered the behaviour.

Has there been any fighting, or just this territorial peeing?

Territorial instincts also may have been set back into place because unfamiliar parties were there for so long. Wick is neutered and litter box trained, but when people come over for long periods of time, he leaves poop everywhere

If litter training habits are lost and it’s not linked to health, you just need to reinstate litter training methods. Move the poops and move the rabbit so they learn again.

When Wick pees outside his box in random areas, it’s typically a signal that something’s wrong with him. Just in case, do they seem fine behavior wise with eating pooping peeing and lounging?

If hes lost his litter training habits since she started marking everywhere, its likely that hes marking now too. Hormonal buns (your girl) can cause fixed buns to act out hormonally if they can smell one another.

Is it possible to have her spay finished now that shes older?

When there is bonding/unbonding sessions, it is definitely common for them to mark via urine, poo and chinning. This normally gets better once they are bonded/rebonded.

It does sound like they reacted to a new scent in the house. (in-laws) and this can sometimes happen when a new routine and/or a new scent is introduced.

It could be the hormone related due to her ovary remaining which is making her more reactive to the changes.

Also, Urinary track infections can cause some off behavior too. I remember when were trying to figure out why in the world I could’t get my two bunnies to bond (they eventually did, but there was a medical issue to overcome for the male), the vet asked me if I thought my female bunny might have a urinary infection as that can actually cause some of this behavior in bonded mates.

But since it seems to correlate with the in-laws visiting then I’m thinking that might have been the trigger. What do the in-laws say about what their behavior was like when they were caring for them?

I would try to work on some prebonding sessions and some stress sessions before putting them back together again, personally. It sounds like the inlaws visiting caused a minor shift in their bond and theyre having trouble cementing that bond again. Minor mishaps like this happen often in some bonds, and not often at all in other bonds. I dont think its anything to worry about as long as youre patient

Stress bonding session would be like mooshing them gently together in a tight space (like a box, with the top open), then setting the box onto a shaking washing machine, or shaking the box gently yourself. If you have a friend, you can keep the buns in the box in the back of the car, and have your friend watch them in case fighting happens or one tries to jump out. Just something short that can stress them out, so theyre forced to find comfort in one another If you do stress sessions, only do one or two per week to avoid stressing them out too bad.

I think at this point, if she cant be around him without acting out hormonally and/or going into a false pregnancy, it isnt going to work. It sounds like, for her health, she would be better off as a single bunny.