I have been stuck on my line of the Crawford family for some time. It seems all information I locate is sketchy at best.

I am searching for information on my ggg-grandfather:
John Brown ALLISON b. 20 Sep 1828 in MO;

His wife, my ggg-grandmother:
Elizabeth Mosbey WOODSON b. Dec 1826 in VA;

My gggg-grandfather (I believe based on the 1840 census): Alexander ALLISON b. 07 Jun 1802 in PA;

And my gggg-grandmother:
Jemima CRAWFORD b. 1811 in VA.

I'm mainly looking for Alexander ALLISON and Jemima CRAWFORD. I can't seem to find out who they are or where they came from.

Any help would be most appreciated.