REDPATH AND DONKIN/DUNCAN -Where did they go?

[belfordian]

I have struggled with this one for years. Hoping rootschatters can suggest other routes to try! Isabella Redpath born 1837 Reedsford, Kirknewton married John Donkin 22-6-1869 Glendale. They are on the 1871 census at Hetton, Chatton with mother Jane Redpath and 2 sons John b 1869 and James b1870. After that no sign of any of them! There is a family at Chirton which matches with ages and names but not birthplaces and it seems unlikely that John changed from ag lab to mariner with no seafaring background. I have searched everywhere I can think of. If they emigrated where can I find records for ships departing from 1871?

Can anyone suggest anything else to try? Would appreciate some lateral thinking!
Val