We just split a property now, we only own a pretty basic single family home at the moment on more trust and handshake for the time-being, but I know as I want to leverage his cash and ask for more, he is going to want to have things laid out in more detail that make him more comfortable with the arrangement. 

Plus, there will be no property management fees, and he will even provide free labor to update the efficiency (as approved).We've discussed that the unit would have to be easily convertible back to a LTR should he leave.My question to the BP community is this: Is there anything else (beyond what I've mentioned and the standard needs for leases) I should be considering when drawing up a lease for this arrangement? 

In that arrangement, you keep the same tax-sheltered benefits of the Roth IRA, but just open up the possibility of the Roth investing in a syndication or note. 

Are there any verbal agreements or arrangements between the current Landlord and Tenant?

Other legal arrangements I need to take care of before I get started?

It's not unethical if you don't have an exclusive arrangement. 

In my eyes with this type of set up make sure that all parties understand that this is a "business arrangement" and not "a family adventure" other wise people will get upset and feelings will be hurt, and we all know how the family gathering will go after people start getting their feelings hurt.Good luck and I hope all goes well.

Quote from @Dagan Flowers: Redeveloped a mobile home park into duplexes.

I'll assume that you have buyers that you know and are working with to find the kinds of properties they want.For the most part, my buy and hold buyers are okay with this sort of arrangement, but my flippers who need a quick turn around would not be.

There may be a cash for keys arrangement you could work out to accelerate a win-win with the tenants.