I am sure we are related somehow. But not down this line directly. My Agnew PA ancester was John Patterson Agnew and I have no idea yet who his parents were. Trying to find out. He is not easy to find at all. He also supposedly married twice before he married my great grandmother so again hard to track.
If you have access to Ancestry.com this is how I got all this information. There is also a family tree (dates in this are a little more accurate though). You can get free trials at Ancestry.com for like 2 weeks. If you buy Family Tree Maker 2006 (under $30) you can get a 3 mon access to it. The yearly access for US info is like $150 and the World info is like 300. So getting Family Tree Maker saves a lot. Someone clearly did a trace. Might have been the Johnston side somewhere as that is fairly detailed. There is a lot of info on Martha Johnston (your great, great grandmother) and her family. She had lots of siblings (she was one of 8)
According to both the 1930 and 1920 census for Hopewell, Beaver County, PA, John Simpson Agnew was the son of Emmet or Emmit C. Agnew (he was a laborer who worked in a Steel Works plant as a tube worker - 1920 census) and Ethel R. Agnew. Emmet C. Agnew was born in Hopewell, Beaver County, PA and is the son of John C. Agnew (Mar 1855)and Martha J. Agnew (Apr 1853) according to the 1880 cencus. Martha's maiden name was Johnston.
John C. Agnew's parents were Archibald Agnew (Abt 1823) and Mary J. Purdy (Abt 1829)
Archibald and Mary J. Purdy had 3 kids Margaret (Abt 1848), John and Samuel (aboout 1840)
John C and Martha had 7 children (all alive in 1880). They were Archibald (Archie) Purdy(Jul 1878)(Archibald married his third cousin once removed. After the death of Nellie Irene Robb Agnew, Archibald married Sara Agnew), Charles B. (May 1880), Mary J (Apr 1882), William J. (Jul 1884), Sadie (Aug 1887), Margaret (June 1890) and Emmet C. It may be his name is actually Emmel. Hard to tell. (The family tree at Ancestry.com lists all the people that all the children married and their kids as well)
Emmet (Emmel) and Ethel had 3 children John S., Edith J. and Sarah M.
Edith J. was probably born in 1918. Might even be Aug if the census from 1920 was right and she was 1 4/12 old in Jan 1920.
Sarah M. was probably born in 1923-1924 range. Couldn't tell you much more than that. Census results end then.
However since we know Ethel R. Agnew's maiden name was Simpson and according to the 1920 and 30 Census she was born in PA probably in or near Hopewell. I checked for her according to her maiden name and low and behold found in the 1910 census for Hopewell, Beaver County, PA the following.
Her father's name was John P Simpson. He was born in Pittsburgh, Allegheny, PA. His father, John Simpson, Abt 1840, was Scottish. He seems to have been fairly well off for the time as he had a domestic servant and two painters in his house at that time. He had his own business but it is hard to make out in the 1870 Census. Might have been a landlord. Hence the servant and two perhaps renters in his house who were painters. His mother Elizabeth Ann, abt 1841, was from PA or England depending on the census you look at. The earliest on I could find says PA though.
He was a farmer. When he was 12 he worked in a hotel (again the connection to dad being a landlord or hotel owner) according to the 1880 census. He was born between 1867-1868 in PA. He had a sister Lydia Anna, Abt. 1860, a brother Josiah, Abt. 1864, a sister Elizabeth, Abt 1870, and a sister Jane, abt 1876.
Her mother was named Sarah M. Hence your grandfather's sister's name probably. She was born between 1869-1870 in PA as were both of her parents.
Her parents were married in either 1888-1889 in PA.
She had a brother William H. Simpson who was born in 1890-1891 in PA.
They had a third child who died before the 1910 census.
They also had an 11 year old named Peter Smith who was a lodger in their house in 1910.