Hi Ruskie, Karen and Elizabeth,
I've had a look for the Jane McGavin (the housekeeper) in 1871 and can't spot her - but as you say, maybe she had married in the meantime.
As far as I know, of the Skelly children, there were only Margaret, Janet and Adam who had children. Adam only had one (my gtgtgt grandfather - with no mother at the moment

) but Janet and William Thomson did have a daughter "Jane C" b1849, so she would only have been 12 rather than the 16 years old Jane on the passenger list.
Another possibly interesting little snippet is that I was googling variations on McGavin, Thomson and the Clyde Galvanising Company and in google books found "The Jurist" 26.1.1861 "Scotch Sequestrations - The Clyde Galvanising Company, Mavisbank, Govan, Lanarkshire" - which I think means they went bankrupt

. Maybe that would help explain why they left Scotland? I also found an Australian article which said "Robert McGavin of the CG Works, Glasgow was granted a Victorian patent in 1859 for making tiles with "transverse ridges or corrugations of a curved or angular figure"" which was apparently known as "The McGavin Improvement" and these tiles have been found on roofs in Australia.
I'd like to try and find out more about the Galvanising Works, but I'm sure it must be "our" Robert as in 1861 William Thomson (his BIL and business partner) describes himself on the census as an Iron Merchant.
I must try and work out how to search more accurately on google though, as there is an actor and a vet who keep cropping up regularly!!!!
Janet