There are several items at the SC Dept of Archives and History that may be of help to you.One in particular is a will typescript for MITCHELL,ISAAC OF ABBEVILLE COUNTY. It mentions his son Isssac. It also mentions a daughter, Cathorine...but wifes name is....it looks like Maryay.
Use this link to the search launch page for further research. Try different spellings for John, Catherine and Issac as there are many records. Hope this helps. Deb.