Probably already noticed this in the 1920 census, but I'd be looking for a Felix W. Swallow (abt 1860 Indiana) as John's father. He appears next door to your John & Ethel. However, it would appear that Felix may have remarried as his wife Alice doesn't appear to be John's mother. The mother-in-law, Mary Ann Petty, may be the mother of Felix's previous wife. Note she was born in Mississippi the same as John's mother. I did a quick look for a Felix Swallow in 1900 and 1910 but didn't find one.