Mt. Airy was the estate of Benedict Calvert who was the illegitamate son of the 5th Lord Baltimore who gave it to him.
He was a friend of George Washington and his daughter married John Parke Custis and their granddaughter married Robert E. Lee. Washington visited Mt. Airy a number of times including the night after he resigned his commission in Annapolis. He was critized for that as Benedict was a Tory.
Another of Benedict's children ended up in Riversdale which is now open to the public and is also in PG County.
I can't help with your questions, but I thought you'd find that interesting.
Jim Collett Descendent of Benedict through his son George