I may have missed your answer on the thread as there's quite a few pages - have you found the family in 1921?
Evelyn & Frank are old enough to be on their own or married - do you know if they married before 1921?
Jean and Douglas I assume should be with their mother Frances bn 1881
For info. added the 1912 baptism of their son Douglas - can't make out their address 10 D? Street
First name transcribed Taylor original reads Douglas
Douglas Roland Martin Birth 13 Mar 1912
Baptism 28 Jul 1912 St Paul, Brixton, Lambeth,
Father Frank Martin, reed maker Mother Frances