I'm not a theologian but here goes. Doesn't righteousness mean right living, holiness means a cut above, and virtue means behavior showing high moral standards? I want all three!
If God is holy (a cut way above everyone), then can He order the death of anyone? Yes, since all are sinners then death is deserved by all, and God can kill as He wills. Because we rebel against God, we deserve to die. Death is the penalty of sin. It's by His mercy that anyone lives. Somehow, we have to pay for those sins. That's where the Christian faith comes in and claims that our sins can be paid for by grace through faith via the cross.
In other words, since all those kingdoms in the Canaan were unholy, they all deserved to die. Therefore, God could kill them as He led the Israelites through the land.
Original sin is not easy especially in terms of babies, and I don't know if I can explain it.
Can I still die (martyrdom or other reasons) even though I'm righteous and virtuous, and holy? Yes. I'm not sure how to explain all this either. But we have a great afterlife policy.