How to clean this house filled of cat filth?

After you clean with bleach, air the house out really well (and be super careful with the fumes while cleaning). There are cleaners made specially for dealing with per odors - that would be even better to use. You might have to do it a couple of times before the odor is really gone. Replacing the flooring and any other fabric in the house will help a lot. Wash down all the walls as well and then use a really good sealing primer before you paint. If the attic has insulation in it, that might need to be changed out, because the smell could have penetrated it. If the ac/heating unit has filters change those out as well.