I, too, have read the book, and agree with your summary.I wish to expand on the "other" William Brewer you mention.I have identified him as 1818 (year of death) William Brewer of Oglethorpe Co., Ga., (place of death), who married who married Elizabeth Holman about 1780. They were parents of 1858 William Brewer of Macon Co., Ala., and 1853 Matthew Brewer of Choctaw Co., Ala.
William Brewer and Elizabeth Brewer were executors of the estate of 1799 Burwell Brewer of Oglethorpe Co., Ga. 
The obvious question, of course, is which William Brewer was the executor.Clearly Agnes Paschall talks about her brother William, and I agree he seems to have been born about 1778, which means he would have been barely 21.I have been back and forth on the issue as to whether it is the William Brewer who died about 1860 in Clarke Co., Ga., or 1818 William Brewer of Oglethorpe Co., Ga., who was the executor, but have not found really good data.Agnes said almost nothing about her William in the book, as you note.
Thank you for your post.
NOTES Family Bible of Ann Bates Brewer, NSDAR.She was the wife of 1858 William Brewer of Choctaw Co., Ala. [2}See my post on the Brewers of Sumter Co., Alabama at http://genforum.genealogy.com/brewer/messages/7470.htmlhttp://genforum.genealogy.com/brewer/messages/7470.html Oglethorpe Co., Ga., probate case #89.(FHL USCAN #1893076)Copy furnished courtesy of Linda Bates Essary.