If Jeremy committed the crime do you think he would have hade a better chance of getting away with it if he just left WHF didn't call anyone, then just waited for the farmworkers to discover the bodies?
Obviously a better chance of getting away with it than by committing the errors he did and then notifying police himself.
He still would have been faced with a serious problem when Julie cracked, had he both not told Julie anything and made the bodies be found naturally there would have been far less evidence against him. putting the moderator away still would have been a problem though in that it would revealed an attempt was made to frame Sheila by leaving the gun on her but she can't have done it.
An inept framing of Sheila still hurts. He would have needed to stage it as a break-in if not framing Sheila to have any real chance of getting away with it and that has its own pitfalls because killing the twins in their beds would not be consistent with a break-in. He would have needed to get the victims up and then to shoot them. Burglars don't go room to room shooting people in their sleep- people sleeping are not witnesses. Plus a burglar is not going to be likely to use a gun from the house to kill everyone they would bring their own weapon.
Without Julie's testimony and without Jeremy calling police you would have evidence that someone decided to assassinate the family and tried to frame Sheila. If the moderator was left on the gun and it was no where near Sheila so no attempt to frame her then they would simply know it was an assassination. The only one they knew who would profit from that is Jeremy and he had no alibi so motive and opportunity. He would be a prime suspect bu in some instances they don't try you with such evidence hey wait hoping to develop more down the road. That could be sufficient to convict but might not be enough it really depends on the jury you get. It is far less evidence than they had with him calling police so definitely would be a better position to be in though it is still somewhat risky. Obviously if he didn't attempt to frame Sheila
If it were successfully framed as a break-in then it is unlikely he could be convicted. If he screwed up making it look like a break-in then he is not in a good position because who would have a motive to kill everyone and make it look like a break-in? Only Jeremy. The best way to make it look like a break-in would be to obtain a different weapon to use than the one from the house and wake the twins up and shoot them out of bed.
When you add Julie's testimony to the mix no scenario is very good but surely it is better without him admitting he knew about the murders and botching the frame job of Sheila because then Julie's testimony has some validation.
Julie testifies he was planning to kill them when they were all staying there for the inheritance and he called her to say tonight was the night and admitted he was responsible. It is suggested the murderer tried to frame Sheila by hiding the moderator and leaving the gun on her. Who would want to assassinate them and try to frame Sheila? Only Jeremy. Are things great for Jeremy? No but with him calling police and thus establishing he knew about the crimes it is even worse.
Things are best for Jeremy if it were successfully staged like a break-in or successfully staged like Sheila did it because then there are other possible killers besides him.
If you spend a long time telling someone you want to kill someone- then don't kill such person. If you want to kill someone don't tell others about it. When you do you are setting yourself up for failure.