Setup: Single full alien mother with two half-alien (with powers, but maybe with hair) identical teen twins. The "fun" part of course is that they all will look very alike... but their disguises will be completely different. Trying to claim that the sisters are identical twins when the neighbors visit.
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Family trees:
Young
Pearce
Niner
Basically yeah. Though i am altering the concept a bit. Roomates, one a scientist, one a style icon. The fun part is that the scientist spends her life trying to find aliens, and her roomate is one, and she doesn't know it...