I also descend from Walter and Mary Beatty according tot he research done by Marvin Beatty. Marvin has since passed away (December 2004) and additional Beatty additional information which he did not research has become scarce.
In his published book, "The Beatty Connection" he has quite a bit of information regarding Walter and Mary (Miller) which are the patriarch and matriarch beginnings of his research.
He did not document Andrew as one of Walter and Mary's children, but did concede there would have been some he could not document.
The family website exists at: http://www.beattyconnection.com/index.htm
, but has not been updated for quite some time.
I am very interested in knowing how you were able to determine your ancestors also descend from Walter and Mary Beatty.
In my research I have been able to google Walter "Beaty" and come up with some documentation regarding his service in the Revolutionary War in other books as well, but not where he was actually born, nor his parentage.
I have a feeling Walter's parents may have come directly from Ireland as many of the "Scotch Irish" did who settled in Pennsylvania.