Hi,
I haven't found a lot more to link the families but I have a few dates that might come in handy later on if you expand on the family.
1841 Martha Hiscox age 3 is in the household of William Clarke 50, Eliza 25 and James 15, no relationships given but possibly Eliza and James are children of William and Martha could be the daughter of Eliza. Batcombe
1851 Martha Hiscox is living at Batcombe with James and his wife Fanny their daughter Elizabeth 8 and nephew John aged 12 and father William Clarke 73.
She is described as niece which would make her the granddaughter of William Clarke, thus the daughter of Eliza. Martha is age 13 born Bath. I cannot find a Bath registered birth but there is one for Martha Maria Hiscox 4/1837 Shepton Mallet which would cover Batcombe.
In 1861 Martha is living in Batcombe with the Vallis couple and possibly her daughter Sarah Hiscox aged 2. Birth reg. 2/1859 Shepton Mallet Is this history repeating tself with illegitimate children.
More to follow