Sorry to hear about problems with your dad hope things get better again soon.
I'm the flea indicator in our house
We've had problems with our dogs, never had a problem before we took these on, it's me that gets bitten, never him, so nothing was getting done apart from treating the dogs, we had wood floor with carpet on top, he said the dogs needed the carpet. I was convinced the eggs were down between the floorboards as well (floor swelled the shrunk when we were flooded, so there are slight gaps).
Eventually I blew my top, carpet went out, vinyl flooring in, small area of new carpet for the dogs. problem over.
.... Until recently, dogs treated again, bit of carpet is vacced regularly, I think i may now be being bitten when I put my wellies on? is it possible for them to live in wellies? they got sprayed with 'indorex' flea killer and covered with plastic. I'm wearing a cheap version of 'crocs' and haven't been bitten since, but haven't put my boots on, prefer wet feet :-)