No it isn't. See my follow up post.
It was not conditional and hence the same rule would apply to the parents as to God.
Yes, it was conditional. You made it so with your premise that God must be totally omniscient. And therefore no, the same rule would obviously not apply to the parents, unless they are also equally cognizant of the results of their action before they enact it.
Moreover, the omnipotent God - remember you said he's omnipotent - retains total control over the murderer's ability to act. The parents do not have any such control.
Willful inaction is an action.
So, you believe that evil is nothing more than breaking an arbitrary rule as opposed to a state of being?
My belief is irrelevant to this debate. But, fwiw, my view is that evil is defined by the properties of existence. If existence is dependent on an omnipotent god, then evil is defined by that.
Was Charles Manson evil or just a breaker of an arbitrary rule commanded by God?
From a Christian perspective he was both. All men are evil in Christian theology and he also violated several arbitrary rules explicitly commanded by God.