There’s a company called Assurant that you can use to help mitigate your risk.

As long as you put in the work you can be assured your DM campaign wil be successful!

If you let this worked move into your place, you again have no assurance that the work will get done.

I assure you things will be pricey on that old of a property.

what assurance should i ask/look for to make this deal possible/ reasonable? 

If you are new to renovations I would highly suggest pulling a permit so that you have some assurance (inspections) the work that is being performed is to code.

rents would be over 2k per house or door if that was the case and I can assure you rents are not that high. 

I'm guessing they were looking more a lot more assurance that you wouldn't be raising rent, or kicking them out anytime soon.   

I have customers who won't pay past 60 days so puts pressure on me to assure my vendors bill me timely, and in my service agreements with them have same rules in place.

I disagree that the 1065 would be the more complicated route.Relying on each owner to report, accurately, their share of rental activity on Schedule E, plus issuing 1098s to the parties not named in the mortgage would be more complicated and more prone to error, especially if it's being undertaken in a DIY manner..I concede a 1065 would be more expensive than DIY tenants in common, however it frees up the owners to pursue higher value activities and provides them greater assurance everything is being done as accurately as possible.If we want to say error is being mitigated by a tax pro doing the returns of the owners in a TIC situation, sure we can say and all agree to that, but IMO the compliance fees for a pro in this situation for all individuals would be higher than that of just engaging a pro for one 1065.