Hi,

Wills posted online will not even begin to skim the surface of available materials on the slaveholding family you are documenting.
You are lucky in that the Alstons were major, not minor slaveholders in Halifax, and there has been a fair amount of research done on Butterwood plantation.

I would start with tax records and tithables for Halifax.
Slave names were often recorded by tax collectors.
I would check with University and Library archives:

Alston Family papers (#4855) in the Southern Historical
Collection, University of North Carolina at Chapel Hill.

Denise