I have been a landlord since I was 26 (over three decades). I never accepted Section 8. I have nice homes and there was no profit in turning it over to someone who would destroy it.
That being said. If I were the down stairs guy, the first thing I would have done was sue the owner of the upstairs unit. Not the tenants, the owner. No quicker way to get the tenants out. It would not be about winning the suit. It would be about harassing thw owner to get something done.
I don’t know if suing the landlord would have evicted these tenants any faster. When it comes to Section 8 and the other housing and public assistance programs, the decision to evict rests with the bureaucracy that administers the programs, not with the landlord. From what Dad’s friend said, the whole process is one lengthy stay in hell. And if the bureaucracies won’t agree to the eviction, the landlord is stuck with these tenants.