@Fidgetcetera First, flea killer gel, which you dab onto the scruff of their necks, where they can't lick it off.

(A dab of butter on a paw can help distract them.)

Next, get some diatomaceous earth and dust masks. Sprinkle that on all carpeted surfaces & upholstery. Then vacuum up thoroughly. (You might want to isolate the kitties from dusting & vacuuming.)

Lastly, wash all your clothes & bedding.

That should take care of the fleas & their eggs.