Our side of the family spells the last name as ISBELL.
I have a Ann Nancy Martin, who went by 'Nancy'. She married Livingston Isbell. He died and she married James Davidson. She was born 6-11-1753 in VA. Her parents are Joseph Martin & Susannah Chiles. James and Nancy had 2 children I know of: William and Harriett. Since this is not a direct line in my family I have not researched more than this on them.
You may want to check out the posts on the ISBELL board if you have not done so. There is much more information. The families are the same, just the spelling changes over time and area.
Good Luck.