Quite a tangle, aren't they!
I would guess given the gaps in the spacing of the children that around the time Esther was born (or maybe a bit before), Charles did a runner. As she couldn't prove he had died, and he had been away for less than seven years when she got together with John Black, they don't seem to have married (after seven years with no word from him she would have been free to legally remarry on the assumption that he was either deceased or had abandoned her).
It's possible that she had the various children christened together in 1875 because John had left and she was receiving some sort of support from someone connected with the church. Or she might have converted (this was a nonconformist church). John died or left her sometime before the 1881 census, but I can't find a death in the area for him either.
George Wormwell was previously married! To an Elizabeth, who I think is still around in Saddleworth in 1881, listing herself as "unmarried", with a "border", John Davies. They appear to have had no children, so it's hard to know when they separated.
The Charles who died in 1901 Swindon is the same one on the 1881 census (I've edited my earlier message as I seem to have accidentally added t's into the surname where they shouldn't be), who went by Richings and also Richens. His earliest child was b. East Hendred, Berkshire, according to 1901 ("Hendred", according to 1881), and may be Charles Edward W. Richens registered in Wantage in 1870. There is a Charles Edward W. Richings who married in Cricklade district in 1896 who might be the same one (although he doesn't use his middle names on the censuses).
I think he might be hanging about Swindon in 1871:
RG10/1883 32/55
Charles Richens, stone mason (lodger), 30, b. Cirencester, unmarried, lodging with a family by the surname of Ellis.
I simply cannot find Martha or the first child Charles (Edward W?) Richings on the 1871 census.
You might find something about them in the Sheffield Archives - for example, you could ask them what records they hold for Loxley Congregational. There might be some extra notes on the children's christening records regarding the fathers as it must have been a wee bit unusual - six kids at once, and two fathers, at least one of whom appears to have done a runner and the other who she never seems to have married.
http://www.1911census.co.uk/search/tnaform.aspx - I think Susannah is listed in Oldham in 1911 as Richings, along with Martha Wormwell and Harold Black.
George Wormwell seems to have died there in 1904.
Meanwhile, Charles' possible second "wife" (no marriage, unless they're the Charles Richens and Martha Jennet Lovelock who married in 1896), Martha Richings is still in Swindon with a couple of her kids in 1911.
