In California, the in-laws could apply for a guardianship of the minors. They could ask for temporary orders at the same time they filed the petition. I actually think I could make a good case for them to have guardianship on a temporary basis, based on the facts of the case. The comments that he is like a ghost and can barely function, that his wife is missing but he won't cooperate and got the heck out of town without notification to LE, the midnight camping in subfreezing temps, being confused about the day it was (points to mental instability), getting fired as a result and thus having no means to support the kids, being an uncooeprative person of interest in the investigation of the disappearance of his wife, having had the police called on him before, the statement that his toddler and preschooler are giving HIM the support he needs, instead of vice versa, etc.
Now, he could state, in response, that he has help with the boys from his father and that his father is providing for them. My counter argument would be that the father seems to be enabling his son, does and did not have his DIL's best interest at heart and is helping to hinder the investigation. I would point out that looking out for Susan's best interest is in the children's best interests and that not doing so is bad for the children.
I would also argue that an enabler cannot control a possibly unstable man and is not the best person to provide protection for the children.
Finally, and most important (but related), I would argue that without a guardianship, josh is free to leave his father's residence and go anywhere, with those babies, at any time and given his condition and lack of funds, that could be detrimental to the children.
Would I win for the Cox's? I would predict that in California, no, not right away, with the exception that the court may grant a guardianship to them but allow physical custody to remain with the father as long as he stays with his FIL. However, in Utah, which would be the proper jurisdiction as that is the last residence of the children for the last six months, the Cox's would have a far better chance of getting a "full" guardianship and taking custody because of the feelings in the state about josh and what he may have done to his wife and now, because of the information that has come out about how his FIL tried to break up the marriage, and steer josh away from his faith. With the right judge or custody evaluator, that could prove a boon to a case brought by the Cox's. I'd like to see them try, for the sake of the kids!
On another note, I think it should be policy that children of murdered parents should, all else being equal, go to the family of the victim, rather than of the murderer.