If there is a by-law and it has been breached, any owner (or tenant, for that matter) can take action at Fair Trading then NCAT to have the by-law enforced. And the best part of this is if the majority on the committee – the other couple – choose to defend it and lose, they will end up wearing the costs of doing so.
Perhaps getting someone to explain the facts of strata life to them might obviate a lot of hassle and ill-feeling.
But first, what do your by-laws say?