Found in the Union Dale Cemetery, Allegheny County, Pittsburgh PA, Division One, Section B:
DONALDSON,
Isabella CLENDENIN, 1789-1864
Robert Jr., 1817-1884
Lettea CHAMBERS, 1820-1848
Isabella H., 1845-1863
Pressley H., 1847-1866
Robert Sr., 1776-1856

The above are all on one large stone. I have no other info on these graves. It is not my line.