Towards the middle the gap between the tub and the Tile was getting significantly bigger then a quarter inch.

The taller of the twois 12 feet and 6 inches of clearance.

My tenants informed me on Wednesday, (2 days ago) by text that they think there is a leak in the roof above the master bathroom and sent a picture of what looks like a slight bubble in the sheetrock paint about 2.5 inches in diameter.

There was trash all over , broken furniture , wood and piles of junk ,god know how many piles of dog poop, and an inch thick of dog hair!  

If you happen to have a 1.5 - 3 inch drain that somehow has become corroded despite the fact that water is being run down it constantly (meaning that's actually rare) then it's the landlords problem.

When I got there...the foundation had dropped 6 inches on one side of the house, a pool had been improperly filled in, no ductwork for HVAC....it was so bad.

Go down 6-18 inches and you hit rock. 

Depending on how bad is the foundation state (how many inches you have to correct), is very possible the sewer line will disconnect/break in the horizontal portions.

Shortly after the road was completed, my property with a finished basement that was used as legal bedrooms flooded 3 inches deep, 3 times during very heavy rain falls in one summer. 

So this is a split level with a sunken entrance and the builder did not put in an 84 inch tread.