I agree. How can he possibly plead to lesser charges?
The issues, as I see them, are, he's already admitted to murdering SW, and he said it was in a rage and JMO, he's said that because he wants to try to avoid first degree murder, after deliberation for SW's murder.
It's already known that Nico died because SW was murdered, and that CW dumped the bodies.
That leaves the matter of the murders of Celeste and Bella. I don't see any way he's going to be allowed to try to walk away from their murders.
If he admits he murdered the girls, he then has the problem in that this means he killed two victims under the age of 12, and he was in a position of trust, and at least two of his victims were murdered in the first degree, after deliberation, because if he killed a first victim in a rage, the others murders were committed after deliberation.
I don't feel sorry for him at all, I feel very sorry for his victims. He's created an incredible mess for himself, IMO.
I think the best he could do is pray for a plea deal, admit to all and accept LWOP in an attempt to avoid the death penalty, which is on the table, as it hasn't been announced yet whether it will be used in this case, but if it is, and he goes to trial, that's what he will face.
JMO.