I fear you may have misunderstood my argument. I was trying to get angell1 to say that, if omniscient (and therefore knew without a doubt what each of the three children individually would be), whether they would: have no children, have some but not all children, or have all children. Based on angell1’s argument, I was hoping they would agree that they would pick those who did good things for humanity, and not give birth to the one who would do harm (again, these scenarios are in a vacuum, not one influencing another).
Then, I contrasted this against God’s omniscience, love, and mercy - if God only created those who would do good things, would we really have unlimited free will? And wouldn’t that go against God’s whole purpose of creating us? So we could be totally free to either love Him or reject Him - if He only created those who would love Him, it negates our ‘choice’ to love or reject.
Specifically for your answer, it seems you are following the thinking of St. Thomas, where the actions of the murderer may ‘inspire’ (although the connotation associated with that isn’t good for ‘murder’) the other sibling to be a healer. I do agree with this - God allows evil (consequent will) but then works good out of it. If God wanted to intervene every time someone would do evil, He could, but then we wouldn’t really be free. However, that is very different from saying He wants there to be evil.