One has a 4/2 upstairs and an ADU (2/1) in the basement, but they are not separately metered and doing so is not an option (also, yard is not divided). 

There are cathodic protections on the steel gas mains, and if there is an issue in your meter that could be somehow causing the issue.

Rent is available via Rent-o-meter, zillow, etc. 

Usually, the electric and gas are sub-metered and are always paid by the tenants as well as water and sewer if it's sub-metered.

The duplex has only one water meter.

Also an electrical meter was missing on the outside and I just saw two leading me to believe the building wasn't even a legal three-unit so for the high price my dad and me agreed to pass on this one as well.A few days later I got a rather angry call from my realtor asking me why I keep passing on good buildings and what's going on?

May buy my own down the road if the system works.Also of note - owner has been paying the water bill, it's not sub-metered.

Ideally, all of the tenants would pay for their own gas use (they are currently metered individually for electricity).

You're buying by the square meter but you're renting by the bedroom so your ROI won't come from the square footage, at least not mainly.It's on a case by case basis.

I used rent-o-meter to find a projected rent of $2,500.