Responses
Well, he did make the ring Jennette uses to hide her eyes, so he probably can sense her or something. And he probably does know Athy is the princess. Even if he couldn't see through her disguise, Jenette makes it pretty obvious. Who else would she possibly think of as a sister? And she called her "princess" too. He definitely knows.
... how Mr. Black can't see through Athy's magic. He didn't realize that was the Princess. Her glamor magic fooled his eyes. He also seems to know when Jennette is in town and can only approach when she's there.
He doesn't go near her at her home. If he wanted to manipulate her, you'd think he'd appear in her home.