A little bit more on the family, from the Hunslet Cemetery records at the Yorkshire Indexers site. They seem to be in grave No.8960 (Consecrated), as follows, with dates of burial:
Martha Foster of Hunslet (spinster), 23 Nov 1851, age 19
Rachel Foster of Hunslet (spinster), 12 Jun 1860, age 36
John Foster of Hunslet (married), 25 Sep 1861, age 75
Eliza Ann Foster of Hunslet (child), 22 Jun 1862, age 5yrs 6 mo
Sarah Foster of Leeds (widow), 12 Apr 1865, age 75
Those ages are consistent with the 1851 & 1861 censuses. Incidentally, both give John and Sarah as both born in Hunslet, so unless they'd been working away somewhere, you'd expect to find their marriage in that area.
Eliza Ann - possibly registered Sep qtr 1856, Hunslet, no mmn.
Possibly in 1861 census at **RG10/3368 fo88 p31, age 4, born Rothwell. Illegitimate daughter of ?? - the rest of the household is William Kerr (44, b Portsmouth), his wife Ann (43, b Lancashire - can't make out the place), Thomas Derham (lodger, 50, b Ellel, Lancs), Mary A (Derham?), (17, b Leeds). In theory, Eliza could just about be daughter of any of them.... But if Ann had been a Foster, might that give a clue to where John and Sarah once lived and married...?
Must go now - I'll see if anyone's cracked it later.
Arthur
** Edit - should be RG9