Info in "Cemeteries of Bladen County, North Carolina, Vol II, SE Bladen" provides the following on McMILLANs:
"Amelia McMILLAN died Apr 10, 1799, age 3 yr., 7 mo., 18 days.
Iver McMILLAN, died Oct 14, 1843, age 70. Wife, Mary, died July 26, 1840, age 64. Son, Daniel L. died June 13, 1825, age 3 yr. 6 mo. Monument erected by surviving sons: Dugald, Ronald, Iver, and Archibald.
The family monument of the parents of John Iver McMILLAN. His father, John McMILLAN, a native of Scotland, died Nov 29, 1820, age 58. His sister, Margaret McMILLAN, died July 29, 1812, age 47. Also a young sister in same grave as her mother. Monument erected by three surviving children: Ann McLEOD (died Dec 3, 1863), Margaret B. McREE (died Mar 2, 1822, age 25), and J.I. McMILLAN".
This indicates that John and Iver McMILLAN were probably brothers.