Helen,
You ask if it was usual for folk to travel back and forth overseas. Maybe not "usual" but it happened and the shipping trade in/out of the River Tyne could easily have facilitated such travel.
North-east England coal was shipped all over the world, and colliers coulds easily accommodate passengers.
Some of my lot went Ireland>US>Canada>Northumberland>Durham>Canada. So that was at least three times crossing the Atlantic.
A trip, say, Newcastle>Hamburg or Cuxhaven or Bremen, was but a little skip !
The streets you mention, I think, were just working class.... just browse around those streets on the censuses, paying attention to the men's occupations- to get an idea of the areas !
Henry signing m/c, Catherine not.... not usual, him maybe needing to be literate for his work as engineman. My lot never signed their name until about 1890s.
By the way, does m/c show them to be bachelor and spinster ?. Does it just say Tynemouth Parish or Tynemouth Parish Church, Christ Church ? Who were the witnesses ?
Do you have any baptisms of the children of Henry.Catherine ? If they married within Christ Church, that may indicate that they were Anglicans, not Catholic etc !
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A while ago I was researching a German family who came to Sunderland area, about same era as Henry did. I was surprised at how many German had immigrated - not thousands but dozens... ( Trivia note... Battle of Waterloo 1815- Priussians/Germans gave big help to British, against the French- so we were pally with Germans until WW1 changed that)
Note that an engineman when he married, but a labourer, on 1851 census ( page ref 2409-169-14) . Engineman covers a wide range of working on/with an engine... including "standing" engine ?
Michael