Wow....this takes me back to a similar nightmare I had a couple of years ago. I have cats, all indoor, but somehow those pesky fleas got in my house. I didn't have any trouble getting them off the cats, but it took us 3 months to get rid of the fleas in our Florida room. I don't know why, but they were contained to that room, and as long as I kept the cats out of that space, we were fine in the rest of the house.
I tried every home remedy - sprays, Borax, etc, nothing worked. Finally called in the exterminators and they took care of it.
I think that a lovely family of groundhogs were making their home under my house, and I think the fleas may have gotten in that way. How sweet, eh?
I now use Advantage on the cats...in case one flea should happen to land on them when they go to the vet or the groomers!!