Is it possible that Hannah was a widow when she married James POWELL? Have you got her father's details from the 1857 marriage certificate?
The birth of Henry James Powell in 1860 gives mothers maiden name as Sansam. James Powell married Hannah Sansom Dec qtr 1857 Axminster RD.
I would think that you need that marriage certificate to get details of their fathers just in case she had misunderstood the 'maiden name' question when registering the birthb