I am not sure about all of that but I agree with Maggie knowing she was going to die as soon as Harry, who was protected, left her body. And I also agree she planned everything so he had a Starborn who was protected from Raith and her death curse would weakened Raith. I think Maggie trusted Harry would be protected and raised by Malcolm, and she trusted that would make Harry a good boy.
I do not think Raith knew about Harry. He may have suspected there was a child (I do not think he knew the child was a male even) but he could not find Harry because he has been protected, and then, as Mira said, DuMorne and Eb where enough to hide him. Of course, this only works if Raith did not know that Maggie had married Malcolm Dresden. Because Harry is using his name and he is even in the book! So someone with Raith contacts could find him in no time.
I do not remember how Thomas found out that Harry was his brother.
Back to the curse, I agree with Mira, Raith did not know it was fueled by her bloodline. If he knew I think he would have managed to have Thomas killed, one way or another.