Len Sleeman has written the following:

My dad was Martin L Sleeman and lived in the Forest of Dean area all his life. Martin's father was Thomas Sleeman.  Martin had brothers George and Jim and sisters Miriam, Mary, Gertie, Emily and Nora. A younger brother, Freddie was drowned in a muddy pool in the field at the family house at about age 3.
George had a chemists shop in Aberdare.  He had one son Ronald, born around 1914, who lives in Newport South Wales.
Jim emigrated to the US and lived in the Pennsylvania area and was President of the Elks.

Thomas Sleeman died early of silicosis.  He was a demonstrator for the firm who patented shot firing in mines.  After his death the family went across to America to be with Jim and the girls.  The welcome may have worn off when it was realised that their mother had not sold up the old home and so had little money. They returned home, Miriam and Mary lived locally.  Gertie married a Brice and lived in Caerphilly and had two daughters.  Emily married a Trafford in the US, but died early.  Nora went out to look after the children and married her brother in law.  One of the daughters married a Bruffer and that family visited the Forest of Dean and became a pen-friend of Anne in Coventry.

The family tree with all the data I have gathered so far is available as an Excel ('97) spreadsheet.

David Sleeman, son of Jack worked for Ranks in Mitcheldean and in his retirement has been researching the Sleeman family.