Carol, It appears from your message details that diversity plays a tremendous role in your family background.
As far as Denis/Dennis names are involved, I cannot be certain. I have hit a road block in South Carolina. According to my GGGGrandmother, Ruth Pettit Dennnis, the family was Irish...but I have no further evidence other than her word. She married William Henderson Dennis in Tennessee, and began a large family which spread to Missouri, Arkansas, Alabama, Louisiana, Texas, and Oklahoma. There is stories in the family which suggest there is a Cherokee/Choctaw connection but this may have come from my GGrandmother, Sarah White Dennis.
Recently, two of the children of my Great Aunt, brought forward additional information, but the stories brought forward with them are limited to their time frame.
However, many years ago, I found a group of Dennis Family Members which are very much as you described living in out of the way places most people would never believe was habitable.
These Dennis Family Members were multi-racial and are have the same surnames, but are referred to the Melungians. I'll have to check the descriptive name. I learned of the Melungians from someone I encountered in Albuquerque, NM. They were said to appear at the very early beginnings of the New World and were described black slaves, Portugese, and Native Americans who were abandoned or lost when the the early colonies failed and disappeared. They mixed, according to the details, and became the Melungians. I'll have to check again on that description. They may have existed at the earliest explorations of America by the Portugese, Spanish, English, and others seeking the new world.
I'll do some more research to see if I can locate the "mixture" who probably populated the "New World" as early as the Spanish Conquistadors.