Hi Stuart
Yes, the absence of a father's name on an IGI christening entry usually signifies illegitimacy. Rebecca 1847/8 is not on the BVRI.
I think your descendancy chart looks right, and is how I would interpret what we've come up with so far.
I find the BVRI very useful, although others disagree! It depends on the county. Hunts which is badly covered on the IGI has a number of additional parishes included in the BVRI which I find invaluable. I also use the Hunts Marriage Index a lot as it covers most Hunts parishes - this is available from the Hunts FHS on fiche, priced very reasonably. Not having a fiche viewer I have to resort to a 20x magnifying glass and put up with the greasy nose prints on the fiches!
Regards
David