Sweet Pea and potentially temporary buns

It's been a while since I've posted; I'm not really online much these days. Due to nearly every shelter in my area that takes in rabbits being at or over capacity, I've taken in two rabbits from an old co-worker who has found themselves unable to care due to health problems that have arisen. One is a male Dutch (mix, possibly) who is not fixed (confirmed this with a vet yesterday). The other is a female Lionhead (also possibly mixed; I'm not entirely sure). Unless I had her checked for a scar or had an ultrasound done, I can't know for certain if she's been spayed. The old coworker was also not her first, nor second, owner- and he doesn't know if she ever was. I assume she most likely was not. The male appeared to have been dumped on the streets when my old coworker found him running around someone's lawn, so he took him home where he was safe.

I took the rabbits on Friday, and they seemed gonna be settled in nicely for the most part. Had them both checked at the vet and nails were clipped while I had them there. Aside from what appears to be some hormone-driven behavior (ex: mounting and humping my father's arm, and what seems to be a grunting sound and pushing on my little dustpan while I clean his droppings from his pen), Luke (the male) doesn't seem aggressive. I do intend to get a voucher for a low cost spay and neuter at the vet that I can get through my state's House Rabbit Society for both rabbits regardless.

Luke is roughly 2yrs old from I can safely guess; he also seems to have some sun bleaching from being stray. Harriett, the female, from what my old coworker could gather could be around 8yrs old. He had her for about a year, having taken her from a friend who passed unexpectedly, and that home wasn't even her first. She's timid, friendly, and while I swept her pen this morning, had even licked my foot.

These two buns aren't the primary concern, per say. I've had them for two and a half days now. It's more so my rabbit I have concerns about. Yesterday morning, my beloved Sweet Pea (a black mini-lop) was out on my father's lap, and according to him it sounded as though she were growling a bit. Her behavior didn't seem off in the slightest aside from that. However, just this morning, I was changing Sweet Pea's water bowl (she refuses to use a bottle). When I was setting the bowl back down in her cage, she nipped me. Two times in succession.

I had a brief conversation with the NJHRS expressing concern and some advice. I've had a pair of rabbits, unaltered, in the past and when I had fostered a third, unaltered, rabbit neither of my two were bothered by her scent being on me or anything. Since the nip this morning, I've taken to washing up to my elbows after touching either of the two rabbits I've just taken in to avoid upsetting Sweet Pea or triggering any further aggression.

She gets free roam exercise time, and has managed to invade the room the new buns are being kept in due to my not closing the door entirely. She's inspected the two of them from outside the pens, and doesn't ever show aggression or dislike in that scenario.

She supposed to have been spayed, and yet she peed just outside of Luke's pen.

Should I attribute this to asserting dominance over him/both new buns?

Some of her behavior today seemed off, and almost seemed like behavior from an unaltered female. I adopted her from my local SPCA last November right before Thanksgiving, where I was told she had been spayed prior to her surrender to them.

My other question is that I'm wondering if her aggression could also partly be due to the new rabbits being unaltered. Would that be an issue?

I took these rabbits in based on the notion that I would not be keeping them. All shelters within reasonable distance from me are full and cannot take any more rabbits in due to a number of hoarding and breeding instances gone wrong in the Northeast. They are supposed to be temporary, except maybe Harriett (due to her age, we would like to keep her). Though they are, as of right now, temporarily being kept here, I'm not sure what measures to take to bring peace between the buns- as well as prevent any further aggressive acts on Sweet Pea's part.

Again, I emphasize that the new rabbits are not altered, but it will be getting taken care of as soon as possible.

I apologize for the length of this post, but I wanted to present the situation in detail... But I also was not entirely sure how to present all my concerns and questions.

I never had this issue with my first two rabbits, despite them being unaltered. Son for this behavior to come from my spayed female, I was taken off guard.

I think the behavior you're seeing could definitely be due to the scent and sight of these intruders in her house. I once attended an event where I handled a number of unaltered rabbits and later that night my two spayed/neutered rabbits pooped all around my laundry basket where the clothes I had worn were. They definitely knew!

I can't have her free roam 24/7, so Friday night into Saturday morning, she had pulled her little hay house across her cage, her litter pan out of its corner, and left a pile of poop on the hay mat.- and peed outside the pan. I had just been in the others' pens and went right into dumping the droppings into the pan and fixed up her cage all nice again. She hasn't wrecked it since, and she never once went to nip me that time. Just today when I was changing her water was when she got me.

I'm wondering if it won't be a worry after I get the two buns spayed and neutered. It's gonna be a drawn out process, even with the low-cost program the NJHRS has set up. I can get a voucher that knock the cost down substantially (roughly $260 total for the two). I'm hoping I can get a little assistance from my parents to cut it down a bit more. My father wants to keep the female in the worst way. I worry about getting her spayed at her age though.

And if getting them fixed doesn't solve the potential problem with my rabbit, I'm not sure what I could try in order to remedy it.

Yes, having a unaltered rabbit close to a desexed rabbit can make the desexed rabbit act as if they were still hormonal (for example, I had a neutered male who kept on humping and mounting until the female I had was spayed too). The hormonal behavior is very different from one rabbit to another - my first too barely showed signs of puberty before being desexed whereas my youngest rabbit was an absolute nightmare from his 3rd month until he was neutered. Maybe your rabbit was very territorial and agressive before her spay.
The fact that she's defending her territory against the intruders is not surprising either. If you intend to rehome both of the rabbits, there is not much you can do - neutering / spaying the bunnies might help, but it is not advisable to try to make them get along considering that they'll end up being separated. If you decide to keep them, you may attempt to introduce them to each other so that a new hierarchy can be established (it's likely your original bunny will end up as top rabbit, considering she's female, young and was there first) and appease the tensions.
For the old female, it's true that the idea of spaying her at her age is a bit daunting. I would have a good rabbit vet assess her general health before attempting it - it really depends on the state she's in.

The neuter and potential spay of the bunnies is something I intend to do, whether I end up finding them new homes or not... Just simply due to the risks not doing so poses for the future of the rabbits' health. I just feel it's the responsible thing to do. I may get a second opinion from my regular vet on whether or not to do so for the female due to the age concern. The vet I saw didn't push it too much, likely for the same reason of the rabbit's age.

The male does seem to have some hormonal behavior that could be and occasionally is undesirable to say the least. He didn't try nipping or biting the vet, and for the most part he's got a nice attitude for being unaltered. It's just the mounting and humping of my father's arm; he hasn't tried to do so for me. Though I haven't given him ample opportunity to try doing so.

As for my Sweet Pea, she's snuck into the other rabbits' room with me in there, and she hasn't even dropped a hint of wanting to fight or anything with the pens in between her and the intruders. So I'm not sure how to interpret that, if it could be a good thing or a bad thing. If anything, there was just the territory masking she did in front of the male's pen.

I've been researching bunny bonding in case we do end up keeping the rabbits, or even just one of them.

For the time being, I don't want Sweet Pea to think she's not the No.1 Bun in the house because of these two. So when I let her out for her free roam, I haven't been disallowing her from visiting the other two. So long as I'm with her to supervise, she can 'check up' on them, since there hasn't been a single bad interaction with the pens serving as dividers. I thought I could offer her that much so she can adjust to their scents and such. And it seems like she's calmed since allowing her that much freedom. Is it a bad idea for me to do/allow her to do that, even though she hasn't had a negative reaction/behavior in that scenario? (Again, she's NOT left unsupervised when she goes to visit them.)