"what?! Are you insane?!" Alexander yelled after hearing his brothers plan. It was good trying to minimise the level of dark energy inside of him. But he couldn't agree with them testing it out on a human, especially not one with a Vendetta against their family.
Daniel knew better than to argue. Alexander's points were valid, but at the same time he wanted to rid himself of this curse. As long as Jeffery kept on using the Cursed Grimoire, he will be continuously filled by evil. At some point when he'll no longer be able to contain all the darkness, he was going to implode.