I may be able to sort this out for you. First of all, are you certain that the Isaac Miller you mentioned is the correct one? There was another Isaac Miller who was of the same age [1 year difference] and who was probably a cousin of the Isaac you mentioned.
In 1900, this other Isaac was married to Loula and had four children: John H , Joseph W , Minnie M  and Annie E .
Both of these Miller families were in Claiborne Parish in 1860 and 1870. By 1880, both families were in Webster. They lived near each other...at one time they were neighbors. Both wives were from Tennessee. The parents of the Isaac you mentioned were Jacob Miller and Martha J. [Unknown]. The parents of the other Isaac were J R Miller and Elizabeth A [Unknown]. Both men were probably from Wuerttemburg. In 1850, I located Jacob and Martha, but not J R and Elizabeth. Jacob was in Claiborne Parish.
If you can be certain from which Isaac you descend, I can send further information.