In 1920, Issac's brother, Allan Vanwinkle, was living with him in Oregon Co, MO.
1920 United States Federal Census Thayer, Oregon, Missouri Isaac E Vanwinkle 38 head m w born MO fborn US mborn US Martha E Vanwinkle 28 wife f w born AR fborn TN mborn TN Martha E Vanwinkle 12 dau f w born OK fborn MO mborn AR Ethel May Vanwinkle 11 dau f w born AR fborn MO mborn AR Lee Vanwinkle 9 son m w born AR fborn MO mborn AR Cloran Vanwinkle 6 son m w born AR fborn MO mborn AR Dorothy M Van Winkle 4 dau f w born AR fborn MO mborn AR Clyde Van Winkle 0 son m w born MO fborn MO mborn AR Allan Van Winkle 24 bro m w born MO fborn US mborn US
This is a good match for your Issac Alex Vanwinkle from 1900. He's probably the Alexander Vanwinkle in the following family.
1900 United States Federal Census Wiley, Randolph, Arkansas Isabel Vanwinkle 43 head w f widow 7ch 4liv born Sep 1856 MO fborn AL mborn MS Alexander Vanwinkle 16 son w m born Oct 1883 MO fborn IN mborn MO Martha Vanwinkle 11 dau w f born Jun 1888 AR fborn IN mborn MO Allen S Vanwinkle 7 son w m born Mar 1893 AR fborn IN mborn MO Mary A Vanwinkle 5 dau w f born Jan 1895 AR fborn IN mborn MO
The only marriage for Isabel to a Vanwinkle I can find is only a slight possibility, but it's in the right area and around the right time.
Missouri, Marriages, 1750-1920 groom's name: S. S. Vanwinkle groom's birth date: groom's birthplace: groom's age: bride's name: M. M. I. Mccluskey bride's birth date: bride's birthplace: bride's age: marriage date: 12 Aug 1883 marriage place: Shannon,Missouri