Also they don't seem to have considered the witch could be gay. I guess its not mandatory but it seems strange to be that people would form such opinions or prerequisites.
No I meant, she took them in to have a heir but they were boys boys so she decided to turn them into girls. About the cover the witch probably just wanted to be a guy so she turned the boys to girls first before herself so she could come back as a woman the can use the witch powers.
I think things would work out fine if the little brother became a girl. He'd still be able to be the Witch's lover even as a girl, and he'd also become her successor. As for the elder brother, he'd still get to protect both of them.