Have you tried going through the Census page by page? Laborious, I know, but I had to do that to find relatives in a NJ 1930 Census. I finally realized that the correct Census document was missing two pages on the Ancestry.com site. I ordered the microfiche through the Family History Center near me and, sure enough, there was my family on one of the two missing pages. I notified Ancestry.com and they finally added the pages to their site. Also, have you tried searching the 1920 Census for Webster Parish, using just a first name? Also laborious, but I have had luck that way also. Have you found the family in the 1940 Census? Are they at the same address they were at in 1920 or did they move? Maybe you need to try a different portion of the 1920 Census for Webster.