very resistant fleas on only 2 out of 4 cats

I live in a multi cat household where only 2 of the cats seem to be suffering from a flea infestation even after treatment. Advantage for large cats worked the first time they were infested last year. This time it worked but they were reinfested after just a week. so I gave them fipronil. Nothing. It has been 3 days since they were dosed and I don't feel comfortable giving them more meds so soon but it has had zero effect. At least they do not exhibit any side effects, but I'm really at a loss here what to do! I applied correctly and they did not ingest any of the medicine. The flooring is hardwood and I have washed and sanitized (setting on dryer) all of their and my bedding. I live in northern California where the weather is mostly dry and 65-70 degrees during the day. The house has poor insulation so it is 60-68 degrees indoors. These cats are both fluffy, strictly indoor cats. One is 11 lb, the other is 15 lb. They don't seem too bothered, they are still active and playful, not scratching or grooming abnormally, but I can see the flea dirt and fleas when I part the fur. It isn't too much, but of course I still want to get rid of them! Thank you so much in advance, I will be seriously eternally grateful if someone can provide help on this matter!

you can give them otc Capstar, and talk to your vet about putting them on Revolution

Thanks, I will try the tablets! I guess if that doesn't work, it's no choice but off to the vet. For one of them it's his first time ever having fleas, can't believe they're that resistant to these pricey spot-ons