Keeping them off the bed isn't as difficult as you might be thinking; using a dog ex-pen or two, and some strategically-placed fences/barries made out of NIC grids, you should be able to do it. I know of people who have successfully blocked off their beds in this way, while otherwise allowing free run of a bedroom or other bunny-proofed space.
Your second option: get a tarp or plastic tablecloth (washable) and keep it on the bed when they're out.
Second option, part 2: You can set up a nice, big space for them to run around with one or more dog ex-pens and/or NIC grid fences. These can be moved or folded back, accordion-style, depending on when you're there to supervise and when you're not. Should work very well!
My bun was spayed over a year ago, and even though I'd like to allow her on my bed, I've found that it doesn't work well. Her instincts are telling her that she
has to mark my sheets and blankets. Buns are going to want to mark anything that smells so strongly of you; plus some seem to just
need to pee on soft things, while others could care less... it depends on the individual. In my case, it's just too much temptation for one little bunny!
You've gotten some good suggestions here, and I'm sure you'll be able to figure out something that works equally well for you and the buns. It might take a bit of time to find out what that is, but it's well worth it.
Edit: Oh, and just in case: if your buns aren't spayed/neutered, getting them fixed will help with a lot of territorial behaviors (including marking your bed), though it takes time for their hormones to die down.
