I believe you are doing a lot of the right things by building a team around you, and just know that you don't necessarily need to have everything perfectly arranged around you before finding a deal. 

I would arrange a flat-fee agreement with a local eviction attorney, approach the seller with a purchase price reduction (add plenty of $ your inconvenience), and move forward to closing.There is drama in every real estate transaction if you bother to get bogged down in it.

I would ask for a refund of the last months rent as compensation for the inconvenience of keeping a spotless house, the showings and the uncertainty of your living arrangements as you cannot really plan until it sells...maybe a bonus if it sells quickly due to your “staging.”

I would definitely talk to an attorney or an expert about what other contractual agreements need to be put in place to keep the arrangement going forward worth current renter;  if they are taking care of the place and there are no other issues and rent is coming in on time, I’d take care of the items noted above and that other posters noted and keep tabs on things going forward.  

While this arrangement opened up the price range, the competition increased tremendously with us often going up against deep-pocketed investors or folks making all-cash/non-contingent offers.

Arrange to meet with them and ask to iron out your problems so that you and they will be happy.

But he's a great tenant (so far) and I'm very happy with the arrangement.

We spend a day running around buying the items, then they leave, I stay and arrange them all as she instructed. 

@Jacob Atkinson That sounds like a great arrangement with a significant competitive advantage. 

If doing it the old fashion way, you could always do an addendum stating the terms of your payment arrangement.