fleas are a pain in the butt to get rid of. the key to getting rid of fleas is to prevent them from ever getting in your house. I know it's too late for that, but just in general, once they're on your pet, they're in your house by the millions.
they'll stay dormant in your couches and carpets for months. once you start a treatment course, it will seem worse before it gets better. that's because there is roughly a 3 month life cycle you have to get through while whatever is in your house matures and dies.
I would start by getting some house foggers. set up an appointment with your vet or local groomer to get all your pets a flea bath. while they're out of the house for the day, vacuum your house really well and set off the foggers. read the instructions very carefully, because they can be dangerous stuff.
get yourself a good topical flea prevention. I'm gonna tell you to stay away from the generic stuff and get a frontline/advantage from your vet because while some of them may work - they won't work as well as the name brand stuff - and you have a serious problem. don't cut corners right now. buying the brand name stuff from 1-800-petmeds is buying counterfeit product most of the time. that's why they can sell it so cheap. (compare the INNER packaging from what your vet sells you and what an online pharmacy sells you, and 9 times out of 10, it will look different. I know because I see it all the time at work. people are shocked when I show them. it's a sad business, but with these products being so expensive, and with the economy the way it is, I understand why people need to save the money.)
look into getting a product called capstar if you want to go all out (if you can't get it through your vet directly, ask them if they know where). it's an oral medication that lasts 24 hours - we give it to pets that come into the hospital with fleas. within one hour you can see the fleas falling off the pet, dead. it's amazing. just not cost effective because it's a daily pill. good for 1-2 time uses. I'd recommend giving one of those when the pet gets home, because you can't put your topical on the pet for 24-48 hours after a bath so that the oils in the skin have time to build back up (that's how the topicals travel over your pet giving total body coverage from the few spots you apply)
keep an eye out on your pets behinds. cats and dogs get tapeworms from eating fleas. easy to treat, but can reoccur if you don't get rid of all the fleas.
in a really sever case, if all the above doesn't work - you may want to enlist the help of an exterminator.
good luck. this year is going to be REALLY bad for fleas and ticks. we've been getting warnings about an up rise in tick bourn diseases in people and pets.
let me know if you have any questions! I'm pretty good at counselling clients when they come in with flea problems at work