Moral dilemma??

As background, I am a Lutheran Christian and everything I know about Christianity I have taught myself because my entire family is atheist, and I chose to follow Christ; as a result, I am not super well informed so just wanted to ask this somewhere.

I watched a true crime story somewhere about a man that murdered his children to “secure” their place in heaven.

As a result, I now face a dilemma while thinking over it: Is that righteous? and would his children really have gone to heaven? Would he go to heaven?

My presumption is/was that people who are murdered, especially children, would go to heaven because they never really had a chance to prove themselves or turn themselves towards Christ. My presumption is also that murderers will go to hell.

Obviously I know and believe murder is wrong and is sin, in this hypothetical situation I am wondering what I should think: if you are “securing” and “guaranteeing” spots for people in heaven, while sacrificing yourself to hell? Is that then some sort of righteous sacrifice? Are you then a type of “good” person? Of course not right, but why? I just need a clear answer.

Thank you.