Which father messed her head up (hope it wasn’t Magnus, I kinda like him not tally messing with her) and which parents did she kill? I agree on the sibling ness though lol. There should be a Magnus family comicWhen Lorna was very, very young, she and her parents were in a plane, and her power manifested with a result of making the plane crash and killing them. Lorna surived. Magneto arrived, warned by the magnetic signature, knew her as his biological daughter (from an affair with Lorna’s mother) and asked Mastermind to erase her memories of this.
It may have been out of a misguided feeling that it would protect her to repress the memories (in a way it did; but it’s also blamed for Lorna history of mental instability).