Think you'll find that Keynsham (itself in Somerset) Registration District covers parts of both Somerset and Gloucestershire.
The family in 1891 are in Glastonbury:
Reference RG12, Piece 1915, Folio 48, Page 21
Wood House, Street Road, Glastonbury
Ruddle, John Albert Head M 31 Millers Carter
Ruddle, Ann Wife F 36
Ruddle, Arthur J Son M 9 Scholar
Ruddle, Rachel A Daughter F 8 Scholar
Ruddle, Grace Daughter F 7 Scholar
Ruddle, Louise Daughter F 5 Scholar
Ruddle, Tom Son M 4 Scholar
Ruddle, Selina Daughter F 3
Ruddle, George W Son M 5 months
All born Keynshan, Somerset except the last child George, born Glastonbury