I believe that Vernal (it's both Vernal and Vernon in the census, but I've seen Vernal twice, so I go with it) is the son of Benjamin, born ca. 1792 in PA per the 1850 census of Marshall Co, MS. Other than the notice in Holly Springs, MS newspaper when Benjamin Kizer's estate was being settled, I have no hard evidence of Vernal's parents or siblings. Of course, I've seen what other researchers have, but most people don't cite sources, so I can't prove anything 100%. However, Benjamin Kizer's notice in the paper confirms his birth in PA, which connects from TN to MS.
But here's some things that are documented:
Nicholas and Benjamin Kizer are on the tax lists in Allegheny County, PA in (1786), and they may be related to Benjamin, David, and John Kizer below.
I have this bit of hard evidence for David Kizer, whom I also believe is the brother of Benjamin Kizer; this is from the Nashville Christian-Advocate (you've probably seen it):
May 31, 1844 DAVID KIZER born Pennsylvania, January 29, 1786; moved from there to Montgomery Co., Tenn. in his 17th year; then moved to Henderson Co., Tenn., where he died in the spring of 1844.
I also have a record of a marriage of John Kizer in Montgomery County, TN:
When I put those two records for David and John Kizer together, the time period is exactly right for both of them to have resided in Montgomery County at the same time. This will connect them from Montgomery County to Henderson County.
Benjamin moved around a lot. As I've lamented before, I don't have evidence of a birth record for my g-g grandfather Vernal or even for g-grandmother. No marriage records for Vernal either, not even when he married his second wife. Thank goodness I have the marriage record for Lucinda and my g-grandfather.
Have you looked for Mary Gilliam? Polly was a nickname for Mary.
There are extensive records of Thomas Kizer's military service in the Rebel Archives that can be accessed on fold3.com (formerly footnote.com). He was an officer; I believe he was a sargeant. Nicholas Kizer's Confederate service is very well documented also; he fought at Shiloh.
Right now, this is just about the extent of what I know that's truly worthwhile to someone else. I haven't done a lot with this line yet, but the Kizers were undoubtedly part of the great Palantine immigration, and that's a fascinating subject.