stole children from towns, subjected them to severe torment, messed with their genes, and murdered everything that stood in his way. His total death toll would've probably been in thousands, either by his hands or by his subordinates.
planned on murdering an entire city of thousands of people, including children, stringing them up and using their bodies as a sacrifice to gain the power to rule the world. his death toll is again in the thousands, if he/she had succeded
Had the main hero hadn't come along to stop her, her actions would've left the entire world into chaos, causing civil war and much strife, resulting in the murder of thousands of innocents. Other feats include being a traitor to those around her hurting only people on her side, but even the young. Had the hero hadn't stopped her hundreds of thousands of people would be dead or dying in a very unstable world.
You didn't give us enough information such as how they felt while doing it/what their motives were.
Your basically asking is killing one person as evil as planning to kill two which is difficult to answer.
well pretty much all the people they were going to kill were for the most part civilians and or children. For example person one kidnapped and tortured children, person 2 wanted to kill everyone children, adults it didn't matter. person 3 actions would've led to the slaughter of thousands which would've started a mad power grab which would've wrapped the entire world into total war and death, he/she also was a traitor to his/her clan