My personal opinion is that this situation has you wrapped up emotionally. Don’t take this the wrong way, but the sale is by a party with whom you have some sort of relationship (so you feel somewhat obligated), and you sold 3-4 years before the housing peak so you’ve had to endure some additional ridicule from friends/family than those that waited longer to sell.
My recommendation is to try your best to separate the emotional components of this transaction and view it as objectively as you can.
The first thing to do would be to view the historical price fluctuations of the property, along with all of the withdrawn and canceled offers that have been made over the years. Analyze the comps as a means of upping your negotiating power. It sounds like this home is quite unique, however, and reasonable comps may be hard to come by. So use them when they favor you and discount them when they don’t.
The next thing would be to try to transcend the fact that you have a relationship with the current owners. Without knowing the depth or breadth of that relationship, I would advise that you focus on how the transaction might benefit your situation, rather than how it might adversely affect the current owners’.
Delaying the process a month or so to perform “your research” may give you a wealth of information. Imagine your wife and the current owners pressuring you make a move and fast. This will give you insight into what their position might be in the sale – whether they are more or less motivated to sell for whatever reason(s). It is perfectly acceptable to tell them that you want to take your time in making the investment of a lifetime. Meanwhile, you may have earned yourself some additional savings in the form of reduced home values and/or negotiated price.
The first rule of negotiating is to NEVER lose the power to walk away from a negotiation. Your current situation is putting you in a position that may potentially compromise this rule, so you must work to overcome it.
I wish you the best of luck on this, and be sure to keep us all posted.