How to contact last seller needed for sale of property?

[Christian Sharron]

Bit of a long story, but my partner and I are trying to purchase a property from a family friend of mine and we're having trouble locating the last seller. Family friend has multiple siblings (some of which have passed away and have heirs) and they all inherited a 3/2 when their father passed away.  All 17 or however many sellers want to sell, and we've agreed on terms for seller financing, but the problem is no one cannot get in touch with the last reminding person. The family tried and couldn't get ahold of him. We've done a search and have left notes on doors for people who have that name. We reached out to a private investigator and have had no luck. Has anyone else come across a similar situation and/or does anyone have a good PI in the triad region of North Carolina they'd recommend?  Thank you.