You may no longer need the information; however, Posey Alexander, born about 1853, was the son of Matthew Alexander and Juda(h) Anderson. In addition to the second family, he had son Joseph and possibly son John from the first marriage. I have quite abit of information and will share it by email (or will post it here if you prefer).
Neither Posey nor Matthew was my ancestor, but we may be related some 300 years ago. Do you know a male Alexander offspring who might take the YDNA test? Take a look at the DNA web page http://www.alexanderdna.org/ for information.