I have located the following marriages for Barrett's children:
Martha W. Brewer m. Daniel Sanders in Putnam Co., GA Dec 5, 1811 (Mary Bondurant Warren, "Georgia Marriages 1811 Through 1820," p. 259)
Ibid., p. 129: Sally Braver m. William Harden Nov 9, 1815 in Putnam County, GA. Since there are no Bravers listed elsewhere, I assume this to be Brewer.
Mary B. Warren, "Marriages and Deaths from GA Newspapers, 1820-1830," p. 113: Scott, Rev. Benjamin C. and Mrs. Sarah W. Harden, youngest daughter of Capt. Barrett Brewer, married Oct 23, 1825 at Mr. Daniel Sanders' in Morgan County by Rev Benjamin Ogletree.
Nell Bass Riggs, "Alabama's Pike County Marriage Records, 1830-1849:" Brewer, John P. and Susanah J. Townsend, Aug 26, 1833.