If what you think is correct about Archibald and John being brothers then I think I am on the wrong track. Christina Kennedy was my GG Grandmother and on her marriage cert (in Melbourne) her father is Alexander. There is also a Christina Kennedy on the Gengis Khan so will recheck that. I also have contacted one of the historical societies in Argyll and they are doing a search for me.
It is very confusing when so many have the same names!
Thanks for your reply.