I agree there has been considerable misinformation posted online and published regarding the Gilliams.
I have a website that has tried to bring some clarity to the Gilliam lines of Virginia and beyond, entitled the Gilliams of Virginia. On this website I have posted (for the most part) only primary source material with a few editorial remarks for clarification. See www.home.roadrunner.com/~gilliamsofva/index.html
Unfortunately, much of what you have just posted in my opinion, falls into the misinformation category.
Here are just a few examples (see my “Fact or Fiction?” on my website for more in depth explanations):
The name Devereaux was not used in the Gilliam family until after William Gilliam married Mary Jarratt the daughter of Devereaux Jarratt, Sr. This marriage likely occurred in the late 1740s, possibly in New Kent County, VA. Any other suggestion of earlier Devereaux Gilliams or William Devereaux Gilliams or Thomas Devereaux Gilliams is purely speculation and undocumented. It is highly unusual for anyone at that time to have a “middle” name.
The wife of John Gilliam, the Herald, is undocumented.
The wife of John Gilliam of Norfolk is undocumented. It has been suggested that his wife was a Miss Fountayn/Fountain as a Roger Fountayn oversaw John’s estate, but that is pure speculation. It could be equally possibly that Roger was a business partner or good neighbor. His estate makes no mention of a wife, only an unnamed son.
The surname of Margary who married John Gilliam is unknown. It has been assumed she was a Henshaw as John and Margary have a son named Hinchae, but again, this is undocumented. You stated John and Margary had six children. There are four and possibly five documented children: Elizabeth, John, Hinchae, Charles, and possibly, Margary.