The 1891 entry records two families.
The mother of the elder children was Jane Crellin, that of the younger Jane Cromwell.

See births on my web site.
Sarah was born 27 Nov 1879 to Crellin
William was born 22 Sep 1884 to Cromwell

Can not identify a burial for Jane Crellin or a marriage for Jane Cromwell.

The family is at 12 Tynwald Terrace in 1901.

Have not identified the birth of Fanny which would narrow down the dates.