I do not have much information on ALEXANDER families who migrated into or from the Shenodoah Valley. What little I have comes from "The Chalkley Chronicles" which are posted at . There is an index so you can search for specific names. I don't recognize the names that you have mentioned.
I believe (but don't KNOW) that Martha (Alexander) Porterfield settled in Berkeley County, Virginia and I wouldn't be surprised if one or more of her Alexander brothers settled there also. This family reputedly settled first in Chester County, Pennsylvania from Ireland. The research surrounding the family is pretty 'iffy' and needs to be done by someone who is especially interested in gathering the facts and not just legend.
Martha Alexander Porterfield was supposed to have been the daughter of John and Susannah Alexander and the sister of Rebecca (Alexander) Emmit. Although Rebecca's will mentions Porterfield nieces and nephews, I have not seen proof that they lived in Berkeley County.