There are two nieces listed with Andrew Wynne and his wife on the 1900 Census. Have you been able to identify the nieces with the Wynne or Butler families?
I note that the nieces were born in Mississippi with both parents born in Mississippi, which indicates a sibling of Andrew or Nellie was born in Mississippi.
If you look at the 1880 Census for DeSoto County, Mississippi there are two Wynn families:
George Wynn, age 59, born about 1821 Virginia, Mulatto
Wife: Caroline Wynn, age 56, born about 1824 Virginia, Black
Son: George Wynn, age 10, born about 1870 Mississippi, Black
Randall Wynn, age 55, born about 1825 North Carolina, Black
He is a widower with four children born about 1868-1871
Remember the census taker spoke to whoever answered the door. Many times if there was no answer the census taker just asked the next door neighbor. So, the information as to the places of birth for his parents may be suspect. On the 1910 Census Alabama is the birthplace of Andrew's father and mother. Also note that Andrew has been married twice and Nellie has been married three times. Andrew died sometime between 1910-1920 as Nellie is a widow on the 1920 census.