The conclusion here is that you'll be out of pocket for $74,000 - $37,983 = $36,017.If you rent, you'll pay rent only one third of the time or $56,975 / 3 = $18,992 or half the cost of buying.The difference between buying and renting is so large that it'll remain in favor of renting even if you change my assumptions.While the property might increase in value over time (or not) you'll never be able to enjoy the increase in equity since you'll keep the condo to live in it and you can't refinance.Of course, it's always nice to own your own property so that you can arrange and decorate it as you want and it might have a more homely feel.

I guess my concern is that it would create a de-facto partnership or tenancy in common arrangement, and one of the co-borrowers would be renting to themselves personally. 

If you are, try to get a contractor in there to look at it, and if you're out then have them look at the inspection report and give you something resembling a ballpark.

However, the way that things have played out over the last few years--it definitely resembles a BRRRR.

LOL.. like anyone would do this for them.I would never put them on title . or give anyone like this control or ownership in any manner.. a fee based arrangement sure I can see that.. but short of that my experience over the decades is this leads to litigation with minor partner..

Tons of good oversite and security and my buyer is very happy with the arrangement as are the occupants.

You and the seller arranged this without an escrow settlement or title company?

Try to arrange a Skype call.

I fell into furnishing a shorter term furnished arrangement and it sucked. 

I'd love to hear how you arranged everything with your partner.