Fiona – totally agree with Jimmy’s suggested approach, but should advise that whether or not your Owners Corporation (O/C) formally adopted the “Model By-Laws” (i.e. those in Schedule 1 to the Strata Schemes Management Act) in 2006, that Act was commenced 1996 and so those are mandatory for your Plan whether the O/C likes it or not.
Further, the verbal agreement between Units 1 & 3 is of no consequence as Sect 65(B) of the Act applies here.
Finally, I’m not suggesting a “shock and awe” approach, just providing some information to assist you in the negotiations.