Thanks Len.
A marriage off the Island would certainly fit what I know so far.
You mention a brother - do you have a name?
The 1851 census sequence has:
Eary Voar
Charles Killey junior and family
Eary Voar
Charles Killey senior , wife and son William
Eary Voar
uninhabitied
Eary Voar
The children in question.
Charles senior married Margaret Shimmin, 20 Aug 1803 at German
8 baptisms are recorded between 1804 and 1823, all at German and including the Charles junior and William above.
There is none for a Catherine but there is a possible 'hole' in the sequence in 1811 or 1813/4