Have you considered Putting cameras on the outside of property.

Mine can set door codes, message (or call) guests, schedule cleaners, adjust the thermostat, monitor my cameras, & call a plumber just as easily as a local PM can, for 1% of the costI wrote much more about leveraging offshore assistants in this post here.

Did you have a camera run through the line prior to excavating?

On camera, they seem like the perfect young couple and in reality, they are ripping people off. 

Can you do exterior cameras?  

Let's assume they are for argument's sake.You need a sewer line cleaning, followed by a sewer camera inspection, followed by estimate for remediation (if necessary).

I would also suggest getting a camera down in that septic line to see if there are any problems with the leach field and/or pipe (ground may have shifted, possibly resulting in a broken line, or if there are any roots impeding drainage)

They are happy with their iPhone photos or some crappy images from a friend with a point and shoot camera.

I f I was you I would defiantly put fence with cameras ( it will prevent truck to drive very close to houses and damage landscape, + higher price for security).

Will get Outdoor cameras & remote thermostats.