Good Morning and welcome to Just answer. I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
These are most likely tapeworms and these are spread by fleas. First, make sure you are using a good flea control and REvolution is a good one. next , purchase Tradewinds wormer at the pet store. This is OTC and will rid all your cats of these worms. These can only be spread by fleas but I would still treat all 3 cats.
Sincerely, XXXXX XXXXX