Mimi, be careful about putting too much pesticides on the cats- it can poison them. Try not to mix products like Frontline, flea shampoo, flea powder, and spray. If you already Frontlined them, then you don't want to add flea shampoo on them too- besides, then you won't know how much of the Frontline got washed away if you shampoo them.
You might try sprinkling just a LITTLE BIT of flea powder on the surfaces the flea-y cat sleeps on, but not on the cat in addition to the Frontline.

If you vacuum, remember that the eggs will be inside the vacuum bag where they might hatch. Mopping the floors will help pick up random eggs.

I'm guessing that your cats go outside. You can't avoid occasional fleas if they do.