Hi again, on the 1841 census: Andrew 60 fisherman, Christiana 60, John 30, David 15, Helen 15 and Cicla Sindoni 60 ag lab ( I wonder if thats Cecilia Sinclair, sometimes the spelling on these censuses is weird and wonderful ) ) who is present on the 1851 census on the same page as your Andrew and Christian. ( Gray,s Building,s Stromness )
1851 census: Andrew 69, Christiana 69 Knarston,s Close, if you click on others on the same page there is also a Cecilia Sinclair born in Orphir and Catherine Dunnet and Jane Dunnet ( sisters) possibly Cecilia married a Dunnet?
Cecilia would also fit in with the name of one of their children
akc