My opinion:
TN did not want to watch the kids. She called Misty. JR being younger fell asleep early but Haleigh did not. Misty was tired and wanted to sleep. She called Ron to whine. She may have threatened Ron with leaving or worse. Ron told Misty to give Haleigh some oxycontin to put her to sleep. Misty gave Haleigh too much. Ron called Tommy to go over and help dispose of the body. Ron staged the kidnapping.
They are all equally involved. Ron thinks he is outwitting law enforcement by agreeing to testify against Misty in exchange for a plea deal. He knows by now they don't have enough against her to press charges or they would have.
If they do press charges, I believe that Ron thinks he can throw Misty under the bus and that Tommy will jump on the bandwagon to minimize his own involvement, perhaps he even feels he can bargain for immunity? Ron worked awfully hard at trying to intimidate Tommy into keeping his mouth shut....
IMO, Ron can't point the finger at Misty without implicating himself. Misty can't point the finger at Ron without implicating herself. Ron can't point the finger at Tommy without Misty pointing the finger at him to protect/retaliate for Tommy.
Tommy is in the best position of them all, and his lawyers are really working for him, they know he helped dispose of the body and they are trying to minimize his involvment by making it coerced. They probably suspect that Misty and/or Ron had something to do with it, but Tommy is not talking. He is that scared of Ron. And even tho Ron more than likely was instrumental in Haleighs death (if perhaps it wasn't the drug scenario), he has the attitude that he is not going down for something that the "*****" did. (His words about Misty in the 911 call.)
Again, the above is my own personal opinion. Feel free to blow holes in it. I love it when I'm wrong. I get to learn something!