This sounds like the Richardson families that settled in Halifax & Warren Counties in North Carolina. We know of 3 brothers, Benjamin, William, and John, whose ages just about match what you have. I have been doing a great deal of research on those Richardsons, but haven't quite identified exactly where they originated. The descendants of Benjamin Richardson, in particular, who mostly still live in Halifax County, have always been told that they were Native American in origin, and theirs is the line that I have followed the most. I have always felt that Benjamin was probably the son of one of the white Richardson settlers in North Carolina, and either a Native American or African American mother. Ben's 2nd wife, Mary Bass (1751-1844)was probably the daughter of Thomas & Tamerson Bass, of Bertie County, a family also with similiar origins as the Richardsons.
What I am wondering is, how do you know that these were the sons of Elizabeth Richardson? Many of us have been trying to find a direct relationship with the Virginia Richardsons you mention, and would be interested if you have found something to connect them. I have lots of data on the Halifax & Warren County Richardsons that I can share, and I am greatly interested in your research.