I can't locate the two children from that 1879 ship's list anywhere, certainly not in Allegheny County where Spring Garden is located. I can't find death certificates for them either, but that's not conclusive since those started at various dates in different parts of the country.
I do have death certificates for the two children in the 1900 census. Both list parents as William Holt and Anne Hardy, and both said they were born in Allegheny County (Pittsburgh), in 1883 and 1890.
I'm doing this research for a friend. I've asked him if he knows of any other of Minnie's siblings.
I appreciate all the help I've gotten so far.