Even if you took it over for the remainder of the mortgage ($72k) and your family member breaks even, you'd still have to charge north of $700/month in rent and that's really in a best case scenario (i.e. low maintenance, low property taxes, etc.) 

As for a lease, I'd say you should have one even if you're going to charge very low rent - some kind of agreement that lays out the terms of your arrangement, that you would both stick to.

They charge no fees, do no marketing and do an OK job in maintaining the asset.

Take your checkbook, because most won’t take cash and they usually charge a hearty fee for credit card payments.

So if I tried to charge any more than that (like also charging last month's rent), I'd be at a big disadvantage when trying to rent my properties. 

Depending on the situation I usually charge around $300.

For repairs, maintenance, service calls I would think charging a flat fee for the call plus an hourly rate and materials.

We will be making a drastic reduction to selling price soon.I know a hard money lender that takes 3 points and charges anywhere from 10% - 14% interest so I used that for loan numbers/holding costs.Demand is very strong in this area for remodeled, move in ready homes, so I'm confident in the potential sale price.

If the tenant moves out before the 60 day notice then I would charge them through their notice or between the days they are responsible (notice period) to the day a new tenant is placed.  

I guess I need to also compare adding onto the main house and jacking up the rent vs doing the ADU conversion and charging two separate rents.