All Campbell County records were removed to Fulton County, Georgia at Atlanta in 1932. Some of the records have been extracted and remain at the Old Campbell County Historical Society in Fairburn, Georgia. Your gg grandfather Mangrum Calhoun Maxwell did not own property in Campbell Co according to the deed records at OCCHS. Since he died at the age of 26, he probably hod no property to be handled by the courts. There is no record of probate in the records at OCCHS. There is a marriage record in Book A-Campbell Co. of Mangrum C. Maxwell and Eveline C. Mattox on 12 October 1856. Hope this helps some.
B. R. Smith volunteer-OCCHS