I haven't done a lot of reseach into William I'm afraid apart from what I've noted from census entries and bmd's. I haven't researched his marriages with Frances or Rachel. From the death registrations I assume Frances died in 1884 (June quarter Bedwellty 11a p51) age 41, and Rachel in 1892 (June quarter Bedwellty 11a p54) age 46.
From the Blaenau Gwent baptist church's Purchasers of Graves book I noted a Wm. Harris of Tillery St. bought a grave for his wife (name not recorded) on 5 May 1892. Plot R19/G033 The MI's of the church have been transcribed but Rachel Harris not included so I assume an unmarked grave.
Also in the same Purchasers of Graves book a Wm. Harris of Tillery St. bought a grave for a child (no name) on 6 Oct 1883. Plot R07/G015
On the 1901 census I see William recorded as a widower, living at 46 Gray St., with his children Levi, Sarah Ann and step-son David Davis. Gray St. was just off Tillery St.
William's parents were David Harris, (recorded as Harries in some entries) and Ann Rees. They were married on 12 November 1831 in the parish church of St. Issells, Saundersfoot, Pembs.
I have been unable to find a baptism for David Harris. There were a number of children baptised to a David and Elizabeth (nee Beynon) Harris in St. Issells post 1790 but no David amongst them. There were no other Harris families having children baptised in St. Issells at this time. There is however an Elizabeth Harries living next door to David and Ann and their family in the 1841 census at Leverox
The parents of Ann Rees are likely to be George and Hannah (nee Griffiths) Rees. Ann was baptised in St. Issells on 24 April 1808.
Children of David and Ann Harris baptised at St. Issells:
William 15 Mar 1832
Sarah 23 Oct 1836 My gg grandmother, she married Edwin Crook 20 May 1867 in Llanhilleth,
Monmouthshire.
George 14 Apr 1839 (born 31 March 1839)
Anne 17 Oct 1841
Eliza 17 Mar 1844
Hannah 21 Feb 1847
Elizabeth 25 Nov 1849
Thomas Rees 31 Oct 1852
There were also two baptisms for David and Ann at nearby Begelly:
William 27 February 1832 residence Coppit Hall, St. Issells. Fits nicely with birthplace of William as given on 1871 census. It appears he was baptised twice
Mary 2 Feb 1834
Presumably the same Mary Harris who was buried at St. Issells 16 Nov 1836 age 2, residence Leverox
David Rees was buried at St. Issells 5 July 1863 age 62
Ann Rees died in Abertillery in 1881 (Dec qu. 11a p54 Bedwellty)
Hope some of this helps. I started a thread on the Pembroke board here on roots when searching for the marriage of David and Ann.
http://www.rootschat.com/forum/index.php/topic,318977.0.html