It was nice of you to try and help the poor kitty.
I hope you can help him... once you get a better look at him maybe we can help you decide on a treatment plan.
I wouldn't worry much about transfer of parasites from the cat to the rabbits with the exception of fleas. Most parasites are very host specific, meaning they only do well on one type of animal.
Dog and cat fleas are the exception because they have become rather "domesticated" like our dogs and cats from living with humans (and both dogs and cats) for thousands of years so they are more opportunistic and will get their blood meal from the handiest host. If, heaven forbid, the poor cat dies down there, the fleas will leave the body as it cools and will go to your rabbits. They sense body heat and CO2.
As for the ear mites, in cats and dogs you will see a very dark waxy buildup in the ears. You can treat them with mineral oil or even olive or vegetable oil massaged into the ears. I would repeat at weekly intervals for three weeks. A day or two after the first application I would remove as much softened wax as possible and reapply the oil for better penetration of the ear canal.
I would treat the fleas with
food grade Diatomaceous Earth. Simply apply as you would a flea powder. It will cause the fleas to dehydrate within a day or two. You can also sprinkle it around the rabbit cages (and on the rabbits themselves) if you are afraid the fleas have gone that far.
The only internal parasite that I know of off the top of my head that rabbits can get from cats is the rabbit tapeworm. Cats and dogs are the intermediate host. In your case, it still isn't a problem, because the part of the worm that contains the eggs is passed with the stool of the animal and then the segment will crawl up onto a plant. When the rabbit ingests plant matter with an egg case they develop into worms in the rabbit.
