You will need to treat all the animals in the house even if you do not see fleas or flea dirt on the bunnies. Cats and bunnies are very clean critters and they probably groom a lot of the flea dirt and actual fleas off of themselves. If you don’t treat the buns you run a huge risk of not clearing up the problem until you treat ALL the pets. Especially if the topical flea meds make the cats less appealing to the fleas- rabbits might show a higher infestation then.
Safe for bunnies is Revolution Cat or Advantage Cat- NEVER FRONTLINE, and never any of the combo treatments- Advantix, Advantage Multi,etc. Revolution is prescription since it is also heartworm preventative for cats, but Advantage is typically not prescription.
After treating all the pets, you will want to vacuum the whole house especially the areas where the pets are- if they like to go under the bed, couch, chair, etc- be sure to get under those items. Be sure to empty the vacuum afterwords- getting rid of the bag or emptying the canister and getting it AWAY from the house/garage, etc where the fleas can hatch and get back into the home environment.
Any items that can be washed such as bedding should be washed.
Typically to make sure that the flea life cycle is broken and the problem is truly gone you will need to treat all the pets for 2-3 months straight. There are some life cycles of the flea that need to hatch before they can be killed- and that can take a couple of months.
You can call your vet to see what they recommend and what products they carry and if they have any other suggestions for treatment.