The fleas on the cats are not really a big deal (in the greater scheme of things). Use a good flea comb to go over the cats as often as possible, ideally a coupla times a day, if the cats are miserable or you are in a hurry to get rid of fleas. Have a little dish of soapy water to remove the fleas-and-cathair off the comb into.
If you want something chemical to apply to the cats, get one of the spot-on treatments FROM YOUR VET (not the ones sold at open retail) and ask first how much resistance to it there is in your area. I will not recommend a particular one, because while I have had good luck with several, it varies from place to place now. No, I do not believe Revolution is carried OTC. If you want to use it, then it costs whatever it costs (you do not *necessarily* need more than 1-2 months' dose for everyone); if you don't want to spend that much, then don't, just recognize it will take longer and more work to get rid of the fleas.
Unless you have an intractable infestation in your lawn too, the main focus of energy should not be the animals, it should be the house. You have to do it ALL AT ONCE, like on the same day or weekend, and yes if it is a good-sized house it is a good-sized job. Take out and launder EVERY SINGLE THING that flea eggs/larvae could be on -- bedding, laundry that the cats have sat on, all bedding, throw pillows, afghans, dog bedding, etc etc etc. Wash it hot and use the dryer set on hot, for all items that will permit it. Stack the clean stuff in the garage or somewhere safe like that while you work on the rest of the house:
Then vacuum very thoroughly, clean any crud out of between floorboards. Big time seriously -- move all furniture to vacuum underneath it, or do your best with the vacuum's crevice tool on furniture that is not moveable.
Then use a premises spray containing an insect growth regulator (IGR) on EVERY THING. I have used Precor with success in a number of different apartments; there may be other good brands too, I dunno. Spray EVERY THING that didn't go thru the laundry. This includes nonwashable rugs, carpeting, all parts of upholstered furniture including the inside parts and under/on the cushions, the lower half of nonwashable draperies, bare wood/tile/laminate floors, and most especially the crevices where baseboard and other trim meets the floors. Those are the places that flea eggs fall and develop into larvae. If you do not get rid of all the larvae and prevent further development of future larvae, you can't get rid of the flea problem. Mind, nothing really kills fleas in the cocoon stage (when metamorphosing from a larvae to an adult flea) so you need to use one of these IGR premise sprays that has residual action, and repeat after a couple months if the problem is not thoroughly licked. Note that you want to leave the windows open and maybe a fan on and let things dry/air thoroughly before you and the animals return to the living space... for which reason it is best IME to do one room at a time in an apartment, or one floor at a time in a house.
If you seriously SERIOUSLY clean the house -- including all the furballs under the fridge, the drifts of dust and cat toys that have lodged under bookcases, etc etc, really EVERY THING -- and use an IGR spray, the problem will pretty rapidly taper off IME. You may or may not need to do this all again in a month or three, just play it by ear, it just depends on the depth of your original problem and the depth of your original cleaning/spraying/laundering
I have moved into a lot of houses/apartments with fleas, and had them multiply up on my cats to a significant problem, and gotten rid of them 100% with these methods. (With dogs or cats that go outside, you may never achieve permanent 100% eradication but you can at least prevent them from multiplying in your home). You just have to do it very very seriously and thoroughly, and use the IGR-containing premise spray if you want lasting results. (I have tried DE and borax as a substitute and IME they do not do much good, compared to Precor)
Good luck, "have fun",
Pat
