There is an exact Free BMD for Sylvia in 1940. It does seem quite odd that she was born so late, with a seven year gap, but not impossible!
Emma in 1891 is problematic. There are several. This is best on age and location, but by no means certain,
Emma Ashmore
Age: 7 b. abt 1884
Father: George E Ashmore Iron Moulder
Mother Mary A Ashmore
Birthplace: Brimington, Derbyshire, England in the church parish of st. Michaeal, Reg dist Chesterfield.
Piece: 2764 FO: 68 PG 28
Folio: 68
Page Number: 28
People in house:
George E Ashmore 43
Mary A Ashmore 36
Ishmael Ashmore 15
Elizabeth Ashmore 13
Frances Ashmore 11
Emma Ashmore 7
Eliza Ashmore 4
Janet Ashmore 2 (All Children of George and Mary A.)
If you got the marriage cert for 1909 of Emma and Herbert, then it would be quite easy to bring Emma back another generation.
There are some possible deaths for some of the children.