Hi Michelle (and others)
Just getting back into my family history after a bit of a hiatus and found your post. Archibald SIMPSON and Isabella nee ROSS are my great-great-great-great grandparents, so seems we are distantly related! I am descended throught their daughter Margaret, who married John ANDERSON, as mentioned in postings elsewhere.
In my efforts to discover more about Archibald, I kept coming across records of your Alexander PATTERSON and have come to the same conclusion as you - the two families were inextricably linked.
The best link comes from an article in the Eudunda Family Heritage Gallery newslettter:
http://eudundaheritage.com/gustav's_newsletters/gustav_newsletter3_September_2001.pdfOn page 3, is a quote from Christina Ross which I absolutely adore: “If Sandy goes to Australia, then I am going too!”
The reference is given as "Among the Pioneers", the Alexander and Jane Patterson Family History. I have never got around to following it up, but it sounds as though it could be invaluable to your research. I assume the Eudunda history group at least has a copy.
Another useful source MAY be the diary of the physician aboard the ASIA (the ship in which they emigrated in 1839), which is currently held by the SLSA, and is accessible in their reading room. I have found the reference to the sections where the eldests PATTERSON and youngest ANDERSON child died, and there may be other references to the families.
I would be interested to hear if/how you resolve Alexander's birth. I am in a similar position when it comes to Archibald SIMPSON, although the records for my ancettor seem even more scant
Darren