I have no known relationship to either the Glasgow Group or the 'Seven Brothers' Alexanders in Cecil County, but I want toset a possible misconception straight. You may be correct that your family is related to a Cecil County Alexander family because DNA testing is hinting that there were at least two, posssible more, unrelated Alexander families there at the same time.
Alexanders separated from a common ancestor by twelve or thirteen generations should have very similar YDNA profiles as tested by ancestry.com or FTDNA or one of the other labs. In fact, two individuals, one from each branch, may have nearly identical or identical profiles while two others may differ on several markers. As an example of the slow pace of mutation, several of us have tested very close to the YDNA profile theorized for an ancestor who lived at least fifty (50) generations ago.