] (snip) As Lief says, Edward was there even on the honeymoon, as if this was a calculated move which had nothing to do with childlessness. Why Edward? Apart from age and temper, which made him the most appealing of the bunch perhaps, and the one least likely to shine academically, from what can be known. Was there something about the inheritance of the Knight estates that precluded them being inherited by children of Thomas Knight? (snip)

] Is there any hint anywhere about this?

I had understood from various bios that Edward was next in line, as it were. I think that I read in the Shields bio that Edward was selected for the Knights because George and Cassandra thought that James, the first son, was to be the heir of the Leigh-Perrot fortune. It ultimately did not work out for James. The second son, George, was not an option due to his health and disability. So Edward, third son, was chosen for the Knights.