I don't know much about using DNA for family history but you might get some Christian and Sharpe matches that would help to confirm these are your ancestors. When I was looking at possible William Henry Christian candidates I couldn't find a WH Christian who was a mariner of the right age but there was a William Christian son of William Christian who was a mariner and sometimes a fisherman whose father was also a mariner. He married in 1891. It's difficult to prove though as William Christian is a common name on the Isle of Man. Here is an extract of the court order affiliating WH Christian to WH Catherine Anne Sharpe's child. He had to pay costs to Catherine Ann Sharpe.