If you had a 4 or 5 year old car...and every data point said it was worth $10K...and the only offer you had was $5K for it...would you sell?

I wouldn't. 

You are missing part of the story.  You have had to, over the agonizing years, to take on co-owners of the car, having them pay the bills on it, so now you only own a tenth of the $10,000 car.  Not taking that $5,000 offer means that you will need to further dilute your ownership.

I am torn about the scenario we are in.  5 years is far too long.  And doing it on the cheap again is super risky.  It hasn't work out to date. 

Either way, they just have to get off the pot and get going before further delays cause the shorter trial to not get completed within five years from now...