I do these posts like normal people do crosswords. I poked around for an hour.
There are no men named Edward Douglas or Edwin Douglas in the census from 1790 - 1930 in Campbell County, Tennessee. Either your source is wrong, the transcribers goofed, he used a different name None of the above.
If it was a first marrige for both of them, there is an 80% chance he was born 1864 - 1871. I was looking for him to establish his age.
The California Death Index http://vitals.rootsweb.ancestry.com/ca/death/search.cgihttp://vitals.rootsweb.ancestry.com/ca/death/search.cgi has some people with mother's maiden name Campbell and surname Douglas, and some others with Father's surname Douglas and MMN Campbell. I can't tell if any of them match your family because you didn't give any children's names.
There is this family in Campbell Co in 1870 J F Campbell 21 Kesiah Campbell 20 Mary Campbell 1
They are gone by 1880.
There are eight women named Mary Douglas with spouses Edwin in the 1880 - 1930 censues, and two named Belle Douglas with spouses Edwin. None match your description.
There is one Edw* Douglas b. Tennessee with wife Mary and 0 Edw* with wife Bell* (* is a wild card; Edw* will return EDWin and EDWard) in the 1930. He doesn't match your description.
The digitized Modesto Bee has 0 hits for Belle Douglas in 1932 +/- 5. It has 35 for Mary Douglas, but the first three I looked at were for Mary Pickford and Douglas Fairbanks. At 3 minutes each, waiting for them to load, I gave up.
I struck out and quit. Sorry. If she gor her three score and 10, she died in 1939, just before the CDI starts.