If so, does it mention the deceased's family members, especially spouse, children, siblings, ...?

There are many siblings that have to agree to this but if I can get them locked in a certain price how can I make the deal go through discretely?

I was researching a vacant property and found a sibling of the previous owner.

And as an outsider trying to purchase the property, no amount of psychology will work to get the siblings to "act right".Take my advice.

Quick question, is it adviseable to use a sibling as an agent.  

I am in the process of signing a wholesale deal for a single family house owned by three siblings that live in three different states (Washington, Oregon, and California).

Taking care of my parents, siblings, kids, and grandchildren would not be an issue while I am at the company, but afterwards, it would be difficult to ensure that the wealth flows to the next generation(s).

I have siblings that would also inherit this property but they are comfortable with me taking the property as long as they are squared away, e.g., split the difference between mortgage and fair market value among them.

They started high in 2010 to sell this place and the heirs (3 siblings) want to pay off the note and have some left over for profit.

Or even two siblings and a friend or a parent/adult child and a friend.Unrelated people have no bond to tie them, making the relationship easy to dissolve.