That house will have to be gutted when they die or get evicted. I can't even imagine the smell just from 2 dogs shitting and pissing in the house over the course of years, let alone everything else that goes on in there. You would have to pull the carpet, padding, and potentially even the subfloor. I can't even imagine how you would get the smell out after something like that. Probably need some sort of hazmat or industrial type cleaning service to come in.
If his floor pissing is a regular thing (and why wouldn't it be for him), it's entirely possible that it's going to go through the floor and give a piss ceiling downstairs. It would similar to water damage from a leaking pipe. If that house has those drop ceiling tiles in the basement, it will show up pretty quick. If it has an actual finished drywall ceiling, it will take longer but be a much more extensive (and disgusting) repair than just replacing a few ceiling tiles.