I think your questions revolve around the rest of us having separate brains and these brains having developed in ways unique to each of us. Theirs is intertwine

I think your questions revolve around the rest of us having separate brains and these brains having developed in ways unique to each of us. Theirs is intertwined to the point that it's one big brain. Perhaps each girl's own part has individuality, but their development would overlap or inform the other in such a way that they can share thoughts. My point: I don't believe you can extrapolate from "these girls can share thoughts" to "all human thought share the same protocol/mechanism." That said, we all have human brains, and maybe human brains share the same protocol/mechanism for thought.