When you have STR like airBNB or VRBO DSCR does allow that income unless you can provide a previous 12 month rents received or a print out from VRBO.The alternative to that is if the lender or UW will allow the appraisal to use MTR/STR income/rent schedule if the rents and property is common to the area in terms of rent available for the apprasier to show proof.My advice to you is make sure you do your home work and deal with a seasoned Banker or Loan officer that funds multiple DSCR loans per month. 

The plot of land is part of the mortgage, and that company doesn't do construction loans.

After fixing it I would then like to rent it out and get tenants in place, and then refi to a conventional loan without doing any cash out.

Their SDIRA company has agreed to do this... so long as the divorce decree spells out this requirement explicitly. 

Anything i should be looking out for when doing a subject-to deal? 

What should I do?

Don't ever do subject to if you are underfunded2.

I'm working on acquiring a former Adult Care Home from a retired couple, and I'm doing research ahead of a conversation with them about owner financing, which they are open to.

They can fund very quickly on Fix & Flip loans as well.i typically do not use them for long term DSCR deals as they are not always the most competitive on pricing.

Do fees go up or down with less competition?