If his son was wealthy enough to own an estate, then it is likely that James was from a wealthy family and is likely mentioned in a will somewhere. I would suggest searching through any Turner Wills proved prior to 1807 to see if any mention him. The Canterbury Prerogative wills would be the first place to look.
I would also look to see where local Middlesex wills are archived, as many Yeoman often left wills proved in the local courts.
