Here's another list of "what happened?" possibilities:
* disappeared voluntarily
* drug deal gone bad
* done in by family
* murders + suicide
* murder(s) + disappeared voluntarily
* met accidental death; bodies still unrecovered
* saw something they shouldn't have; killed as a result
* killed by person(s) showing them land, or who knew where they
were looking for land and were carrying cash money; robbed in the process
What am I missing? If we go with cui bono/follow the money, family is still right up there, still maybe first on the list, because of the interesting possibilities involved with the will. If, instead, we accept the evidence in the Oklahoman article, drug theories vault to the fore. I've thought many times that, Occam's razor-wise, "disappeared voluntarily" makes the most sense - it also fits with drug-induced paranoia (and the lack of affect evidenced by leaving Maizey the dog), and would explain the missing briefcase. Killed during a robbery - another possible drug angle, too, would also explain the missing briefcase - though if that's the case somebody messed up by leaving the rather easily found $32,000 in the truck; or perhaps they met people either on the mountain or in Eufaula or Red Oak who learned they had a large sum of money, killed them, and disposed of the bodies.