There were a LOT of Kennedys on the Theodore, arriving 8 Dec 1852 at Melbourne.. The problem is that Ancestry only gives each individual Kennedy with their age. You don't get to know how they were related or even if they were related at all. If we could see the actual original ships passenger list, it would be easier to figure out. If they were together on the same page instead of on separate pages they could all be related.
Archibald Kennedy 44
I suppose one way to try to figure it out would be to look up the census for Scotland for 1851.