I also found years ago a reference to another James Crocker born 1800 in Milford on Sea, another watchmaker.
He does have a son, James born about 1820 born Hornsey, Middx or Milford according to various censuses who is also a watchmaker/ thermometer (I think they mean chromoneter) maker. He has a brother, Edward, born 1825, also a watchmaker. They seem to be the Crocker Brothers of Brook Street, Kingston. There is also a son, Samuel and others.
I think that the James, 1800, is probably William Henry's brother but it is pure speculation!
I must order some birth certificates!