Hi
I think most or all of the other relatives named in the will are going to be from Snashall or Simmons lines. Leaving the possibility that there might be only those four nieces who were originally Barden?
Possibly all from one brother, but can't be sure.
I wouldn't worry too much about the Sarah Barden will at the moment, it doesn't seem to be immediately helpful, and could be a red herring.
Another possible red herring

There are two Sarah Baden baptisms in Balcombe, 12 Oct 1735, and 13 March 1736/7.
No parents being named there at the time!
https://www.familysearch.org/ark:/61903/3:1:S3HY-D1VS-SK9