Bron
I haven't been able to tie up any of the names together in any census yet.
I presume you are descended from John as you seem to know most about him?
If so do you have his marriage cert,what did his dad do and what did he do too?
Obviously the name Jenkins is very Welsh and also David as the first born,suggests to me that he may have had a Welsh grandad? So I have checked for the family in Wales too,but nothing found.
By 1891 and beyond most of them will have left home,so it's proving hard to confirm any combiantion of Jenkins's as being the right family.I feel sure they should be on the 1871 somewhere,but where

Will try again later,
Carol