Polycephaly is the condition of an animal being born with multiple heads; it's not just the stuff of fiction, animals of all classes have been born on occassion with two or more heads, and Monster Girls are no exception!
Nagas or Snakies as the people call them in the region were a common occurrence in the wild west, in the modern day most have been killed but a few remain, these two Bandita and Bonita though were a very exceptional... Individual... S.(?!?) Born with two heads, the two girls could not be any more different from each other! Bonita is on left and is a kindred spirit with a love for nature and peace, Bandita is a crazy drunkard violent and aggressive criminal who loves thievery and making others suffer.
Bandita is the dominant sister and as such Bonita has to put up with her criminal acts begrudgingly, typically whining about it all throughout embarassing Bandita making her look like a fool in front of people she's trying to scare. But sometimes Bandita tries to be nice to her sister and put up with her 'hippie crap' once or twice a month; generally when they're doing things Bonita likes though, Bandita obscures her face with a bandana. The disguise probably doesn't help though when you are the only known case of a two headed Naga in the west.
Bandita and Bonita were both good friends with the Centaur girl, Bandita could get behind her when she massacred pioneers (the times they joined Bonita cried the whole way through) but Bonita loves the Centaur girl for her love of the natural world and mysticism. The three of them were in a poly relationship at one time but it just got too weird and they cut it off. And though the two Snakie sisters have their vast differences and quarrels daily, they'll never cut each other off.