My question relates to two websites, each of which is a "Calvary Christian College", however in two totally different locations and unrelated to each other entirely (except by name, and thus domain).

All schools in the state are issued a <school-name>.qld.edu.au subdomain, in this case calvary.qld.edu.au and calvarycc.qld.edu.au.

Now what's interesting is that these domains are crossing each other in sitelinks for searches such as calvary christian college townsville. The green data here is for one school (the Townsville school, as per search term), and the red data is for the other school.

I've put a demotion in for this >6 months ago (we control calvary.qld.edu.au), however we're seeing no change on the results page. I have been able to get the owners of calvarycc.qld.edu.au to submit demotions for our domain, which should go in sometime in the next few days.

What can we do to tell Google that these websites are not interchangeable, despite both appearing as "subdomains" of qld.edu.au?

We can possibly open channels of communication with the administrators of qld.edu.au but will need to tell them what we need to change, and at this point I'm out of ideas.