Can you run two furnaces off of one oil tank, but still have two separate accounts with separate metering?

Sounds like splitting hairs to me. I don't know about your system but mine pumps excess fuel back into the tank all the time the pump runs. Why not just split the bill based on square feet?

Never heard of it, but it must be possible

yes you need a split tandem manifold and metering devices

Yes and then No. The fuel company is simply going to deliver x amount of gallons of oil into the tank and bill/charge one account. You will have to install flow meters on the lines going from the tank to each furnace, a simple task and not very expensive. I don't see you needing any manifolds or any other special plumbing other than to install the meters in the lines. You or someone designated to do so will have to read the meters once each month on the same day and do the figuring for how much oil each furnace has used that billing period. The fuel company will not do this. Then simply deliver the bill to each individual and collect the money Obviously the individual whose name is on the fuel company's account should be the one doing the collecting because they are the one paying the fuel company.

Let me ask you this. Would the renters have their own washer and dryer in the apartment or share a community one? Maybe the answer is no on the meter for each but instead a rental rate based on the size of family per unit. I would think you'd need a mechanical contractor that installs furnaces and they set up the separate lines and meters.