Thankyou everyone for all your help! Do we know if there's any documentation on William's siblings? or grandparents?
Assuming it is the Wigan Underwoods you are interested in then...
William Matthew Underwood b1879 Wigan, son of John Underwood and Mary McAvoy.
John and Mary marriage reg. Wigan Sep qtr 1878. Other children, all registered Wigan unless stated...
Elizabeth Ellen, b reg. Sep 1880 d reg. Dec 1880
Annie Elizabeth, b reg. Dec 1881
Edward Hampson, b reg. Mar 1884 Manchester
Nellie May, b reg. Sep 1885 Salford d reg. Dec 1885 Salford ?
Frances Gregson, b reg. Mar 1887
Florence Ellen, b reg. Sep 1888
Horace John, b reg. Dec 1889
Dorothy Gregson, b reg. Sep 1891 d reg. Mar 1902
Bertha Mary, b reg. Dec 1893
John Underwood b reg. Sep qtr 1858 Wigan, son of Michael Underwood and Elizabeth Hampson. Michael was a railway pointsman.
Mary McAvoy b reg. Sep qtr 1859 Wigan, daughter of William Chadwick McAvoy and Elizabeth Gregson, William was a butcher.