Forgive me if I suggest something you've already tried, but since you know when and where Edward died, have you had a chance to obtain a copy of his death certificate?It should show the names of his parents, if the informant had that knowledge.
What is your source for birth location for "Edward?"
1910 census Jackson Co, AL:
Metcalf, "Edwin" F., h, 39, M(1) 17 yrs, b "PA", AL, PA
" Margaret J., w, 38, M(1) 17 yrs, 7 ch, 6 lvg, b AL, AL, AL
" Delbert L., s, 16, b AL
" Dewey A., s, 13, b AL
[Note, the name of the state Pennsylvania is written out, not an abbreviation]
I ask about source for birth location for Edward/Edwin because on the 1900 census in Jackson Co, AL:
Metcalf, Willim W., h, b Feb 1876, 24, M 0 yrs, b PA, AL, PA
" Bettie, K., wf, b Sep 1881, 19, M 0 yrs, 0 ch, b AL, AL, AL
" Henry C., brother,mar 1874, 26, sgl, b PA, AL, PA
[Birth location for William and brother Henry and locations for parents matches Edwin on the 1910 census]
I see you have month and year of birth for Edward and Margaret, so assume you found them somewhere on the 1900 census where it gives that info.
Happy Hunting (^_^)