I'm not sure what "this" refers to, but assuming you mean if DeOrr lost his life due to something other than murder or any coverup, would his parents be charged with negligence? No, nor should they be. Nor should the grandpa be. Nor IR. IMO. I can't even imagine why anyone would even think there should be charges of negligence. Another example (there are many) is accidentally running over your child in the driveway. Imagine if every time a tragedy happened (without intent and not during the commission of a crime) everyone was charged with some type of negligence.
If the parents lied to LE about how Deorr died (if he did die) and where his body is now, etc., etc., at the very least their wages should be garnished to pay for the resources used to search for him.