Attending the strata committee meetings is not likely to be of much help as only committee members can vote, and owners cannot speak without prior permission.
The lack of notice of the meetings given to the owners has the effect of denying the owners their right of veto of agenda items, which means that owners can prevent a topic from being discussed and voted on by the committee.
Then there is the question of whether the works approved by the committee were necessary repairs, or opportunistic improvements to the penthouses.
NCAT would be unlikely to invalidate committee decisions purely for a technical breach, it would need to be clear that but for the non compliance the decision of the committee would have been different. If there were sufficient owners who would have vetoed the agenda item, then a basis for overturning the decision of the committee exists.
Further, if the committee has gone beyond its jurisdiction and approved an improvement rather than a repair, and it is clear that a majority of owners would not have voted in favour in a general meeting, then there is another ground for overturning the decision.
It would be best to act before the work is commenced, by lodging an application for mediation.