Owners – even EC members can't just annex common property areas for their own use. They are effectively extending their lot space at everyone else's expense. They would need a by-law to get exclusive use of common proeprty areas and even then they would have to compensate the other owners.
Call Fair Trading on 13 32 20 to start the process that will lead to a CTTT adjudication. Alternatively, sit down with them and work out a plan so that everyone in the building has access to storage, even if it means subdividing the storage rooms with cages.