In 1870 all three, John 44, Clarkson 18 and Stephen 71 were living in the same household at Lower Chanceford, Pennsylvania. All give Pennsylvania as their birthplace. What's the evidence that Stephen was born in Wiltshire, England?
The parents you show for Stephen, George Morton and Mary Rigby, look questionable. They were both from Lymm, Cheshire, where they both died, 200 miles from Wiltshire. Without a baptism for Stephen how have you established his parents? There was a Stephen Morton living in Wiltshire in 1841 aged 40 ie 40-44, but your man was living in Pennsylvania at this time