Hi Jenny, I had the same experience with my 10-week-old Holland Lop sibling pair. There’s really nothing to do but keep them separated as you are doing until they are old enough for neutering/spaying. I kept mine in cages where they could see/smell each other, but couldn’t have sexual contact (since you never know when your girl will be old enough to get pregnant, and a young pregnancy can really harm/scare a doe).
Your vet is probably going to want them to be around four months or at a certain weight before they can have their surgery, so just hold tight until then. You’ll have to keep them separate for a few weeks afterwards (because their hormones will still rage for up to a month after), but after that you can start bonding them together. I had a really easy experience, I think because they were siblings and because I kept them where they could see each other. They also had their surgery at the same time, so there was no issue of one disappearing and then reappearing smelling ‘different’.