I NEED FLEA HELP PLEASE!?

I have 3 cats and a dog who all have fleas. My first attempt to get rid of them was the medecine that you drop onto the back of their necks. Still fleas. About 4 days later i gave them all a flea and tick bath. Still fleas. 3 days later, I sprayed them all with a flea mist. This def helped, but they still all have fleas. Please keep in mind that i have also been brushing them all with vasaline and a comb throughout all this time. I also put a flea powder all over my carpets. I even cut the hair of my long haired cat really short! I am afraid if i try anything else on them that it could be harmful to my pets. Someone please give me some experienced advice for a multiple animal flea problem.