John, based on all the evidence we have seen, it appears we don't have any source connecting Lionel Branch to a daughter of Thomas Jennings. We know William married Barbara Jennings, but we do not know which one of William's wives was the mother of Lionel.
I would agree that it is plausible that she was a Jennings. I think we are one source away from proof, one way or the other.
Until we can make this connection, I do not think we can conclude that Christopher Branch was a Gateway.