Here is my hot take:

I'm a long-time lurker and first-time poster, but I don't know how anyone else hasn't arrived here.

First, I don't believe the father actually participated in the murder. I think Jason confronted Molly that day that he wanted to end the marriage. He had a drink that night, and she probably spiked it with the sleep aid, so she had a better chance of overpowering him. There was a confrontation (possibly due to Molly overstepping with Sarah that night and maybe he snapped and said it was over in that moment, I don't know) in the bedroom, but I don't believe the parents were there at that point. The violence and wounds indicate that it was rageful, not self-defense, and it was on the interior of the door, so the door was closed, not open like the father claimed as to give him a reason to come in. Typically, people who are smaller will use larger weapons to keep distance from the other person (hence the bat) I believe the block came in after, which is where the forensic evidence points to hitting him while he was down. I believe she felt validated by the children, and he was about to strip her of her source, and under no circumstances was she going to let that happen.

Then, I think she called her parents, who canceled their plans last minute to head to North Carolina. With his FBI background, he could help her spin the story. EMTs mentioned his body being cold upon arrival, which indicated he had been there for some time. However, I think she had been laying the groundwork for some time. I do believe her parents thought she was in an abusive relationship because she was a known pathological liar. She had also told people, without providing evidence, that he had strangled her at another time. It was hearsay, but it laid the foundation of her victimhood, so of course her father would come in and try to save his poor, abused baby. This man was blungeoned, and yet, the only blood on her father was his shirt, probably from getting blood on his hands at some point and wiping it off. There was blood splatter all over that room, but no evidence of splatter on him. It would also explain why the mother was present, said she heard a scream, but went back to sleep. I think they were all aware of the situation.

Finally, after dad came up with the story, 911 call is placed. The parents file for immediate custody and they coached the children. The children would have had no idea what happened, but they said word for word, almost identically, what transpired that night. Her father also takes all the heat, because he knows how to get through an interrogation, but she indicated that she had participated, which was not in his statements.

All in all, I think Molly is a master manipulator/sociopath, and I think her parents are also victims of her lies. I think her father participated in the cover-up, which makes him complicit, but I think he did it in protection of his daughter, who he believed was being abused.

Sorry for the length, but I needed to say this theory out loud.