The Scarlet Witch
Wanda kept her position despite her fathers disappearance. She tends to be more idealist than her brother, an often mediated between his radical viewpoint and Xavier.
She is engaged in Brotherhood activities partially out of fear of her father who she believes wouldnt want her siding with the humans, and partially because she want to keep an eye on the hot headed Pietro.
She is aware of the acolytes, but does not wish to destroy humans, so she keeps it a secret from her brother so he makes no attempt to join forces.