how did you.... holy crap this is almost exactly how I see them genderbent!! too perfect. the ONLY faults I can find here are sam's eyes (his/her eyes are a greyish hazel, not blue) and I imagine fem!cas as a tad prettier than this. dean is utterly spot on though, like wow.
So great!!! Dean's face and Sam is reading Harry Potter and Cas looks like Dean said something, that she didn't understood. They really llok like a female version of Sam, Dean and Castiel.