thanks avm228
apologies for 1896/1869 typo - now corrected.
Yes WEFS Austin had a twin sister Ada.
In 1891 her place of birth is given as Bow, which sounds great - not that Mile End Old Town and Bow are far apart!
Their father William is also on WikiTree
https://www.wikitree.com/wiki/Austin-9878She, and the 1891 census for William/Sarah/Ada, are shown there.
I'm gradually trying to pool my data from assorted sites (Ancestry / FamilySearch / FindMyPast) onto WikiTree, takes time
But there are so many gaps.
William and Sarah's marriage
Sightings of them prior to 1871....
I've not yet convinced myself where/when either of them died, and am also working on finding William's birth.
But the 1891 census(es) for the potentially identical Williams born 1869 would be a fairly good indication if there are one, or two, families here.