The fleas do not live on the dog/cat - they live in the carpet/furnishings - lay their eggs there - and hop on the host (dog/cat) for their feed
You need to blitz your house with a quality household flea spray - that kills not only the fleas, but the eggs too. Have a look on www.petmeds.com.. or similar
(cheaper than buying from the Vet.. but works, unlike types bought in supermarkets/petshops)..
Take the animals affected outside, get a bowl of water, some white kitchen roll, and a 'nit comb'.. (if you have some teatree oil, pop a couple of drops intothe bowl of water)..
Brush through, rinsing the comb in the water every few strokes, and wipe dry with the paper once any fleas/dirt submurged into the water with the paper. The fleas taken from the comb will not be able to leap back onto the dog/you if dunked into the water
Feed every animal in the house some garlic every day - it is a natural repellent to fleas. Either fresh garlic crushed into food - or a garlic tablet... 1/2 a tablet depending on size of dog
If you have been using Frontline for a couple of years - it might be worth changing to a different type of spot on - such as Advantage.. just incase a change might help?