Perhaps you could treat the back yard. They may be picking up fresh fleas every time they go outdoors, especially if you have a neighbor with dogs who are not being treated for fleas. The very best thing I've found for indoors is to vacuum the carpet every other day without fail, which is a lot of vacuuming, and throwing away the bag. You go through a lot of vacuum cleaner bags, and they cost money, but it works.
I think it is an important topic for a disabled dog who can't scratch. I'm sure your dogs think it's important, too.
Yeah, it's hard. I don't want my wonkers, in particular, itchy, yet I'm also more careful, especially with the brain damaged ones. Sometimes it takes great guns for a couple of months to finally get the evil little monsters on the run. You probably will have to treat the yard, too.
We have trouble finding it now in the form that I prefer: "Precor IGR Insect Growth Regulator 1 oz bottle". It is a concentrate which you use plain water to dilute. I do not like the pre-made sprays (which smell awful). I prefer to mail order the concentrate, rather than put up with smell of the other. Also more economical! You can also get a 16oz container, which usually runs less than $60. The 1 oz bottle is usually under $10, and is often available bundled with a "professional" pump sprayer with wand for a little more.
If you have to also treat your yard, you may wish to get the larger size.
A treatment lasts for about 6-7 months -- Really!
When we moved to Maryland, we either had to drive from Rockville to Baltimore, or get a friend to ship it to us from Florida, as the local home depot did not carry the precor concentrate. The pre-mix stuff gave me a headache, and also (see below) stained fabric.
my only caveats:
Just like any product which you use on fabric, you would want to "spot check" your upholstery (underside/back somewhere unnoticable) to make sure that it does not stain.
Being thorough with this once is worth it! I always vacuumed thoroughly, moving all furniture out. Change vacuum clean bag to new one (if permanent bag, then treat bag as well).
I prefer to thoroughly wash (and dry on high heat) any bedding, rather than treat with chemicals.
You do want to make sure that you give carpet adequate time to dry thoroughly before allowing pets back in room.
You also have to eradicate them from the dogs as well, but chemicals are not so good for them (duh). The same year that I discovered precor, my husband's officemate had two tiny little maltese which became so flea-infested with a very resistant type that one of them began to have seizures from the "dips" which the groomers gave them. Her vet was suggesting shaving them both to get all of the fleas off! She was nearly hysterical trying to figure out how to get rid of them. While her husband was spraying the house with precor, I was helping her bath and comb out the fleas, and even when we put the fleas we were combing out into a dish of concentrated flea killer, they didn't die! We were literally having to rinse the fleas down the drain on one side of the sink, while the other one bathed a dog on the other side. I was thankful that our "cuddles" had not had those "resistant fleas" yet! Someone else had mentioned to us about using oil -- food grade oil, not motor oil. Swear to goodness this worked! Not just to rid them of the fleas, but really made their coats beautiful. Basically doused them thoroughly with it, letting it soak all of the way down to the skin, and leaving it on for nearly an hour -- suffocates the fleas! We bundled them up in towels, and held them in our laps to keep them from licking off the oil. Then only problem was having to wash and wash and wash them to get the oil out of the fur (along with dead fleas). Liz said, it was like a "spa treatment" with hot oil for hair! And no worry about toxicity of chemicals being absorbed through their skin! When I see small white dogs, I think about that pitiful little pair of maltese. I shudder to think how much oil it would take to do the same thing for our great pyrenees!