Question about the Witches of Thessaly

Any reason they couldn't be aligned to both demonic and magical? The character gets the gift from one magical parent and the demonic blood/power from the other parent.

Well, summoning? The magical version?

Having power from 2 realms that way is possible. You can be a magus with Incantation, for exemple.

But demonic blood clearly makes you non-human. This is a neat difference. It's like if you were a nephilim: You may look like a human, but you ain't one.

Summoning the Magical Type is the Way we went.
(We have one of these too.)