Claude's previous use of black magic must be from the spell he cast on himself when he was younger to forget Diana, or maybe he is trying to bring her back to life since then? Especially after meeting Athy in this life and actually loving her as a daughter....
Athy should trust Lucas more... after all, they are friends. The whole lives thing, though. He has magic, so this explains why he is able to 'see' other people's magic?