I am adding some information to your list of Benjamin's children:
Eleanor Greentree Ward (aka Ellen Ward) died during the 1870's; she was enumerated in the 1870 DC Census.
Margaret Greentree Hinton moved to DC after the death of her first husband, Benjamin Hinton, to join her sister, Eleanor.John Ward introduced her to John Hurdle, a fellow military musician and friend, whom she married in 1818. They left DC during the 1820's, and I have not yet located them.
James C. Greentree died before 1810.
Elizabeth Greentree Beall died during the 1870's.Her surviving child married Basil B. Beall, a cousin, who died young. That child, Evaline, had a daughter who married her second cousin, John Martin, daughter of Elizabeth Ward, child of Eleanor.In the 1871 DC City Directory, all three (Elizabeth, Evaline, and Mary) were listed residing together, but I could not locate them in the 1870 DC Census.
Mary Greentree married Arthur Luman. They were enumerated in the 1820 Md Census with one child, but left the area during the 1820's; I have not located them.
Asa Greentree died before 1820, he was enumerated in the 1810 Md. Census.