Items on the agenda
For the EC to pass a valid resolution, they must issue a notice of EC meeting with the agenda for the meeting, with the proposed resolution/s set out in the notice.
For example, if the EC were proposing to enter into a building contract, you would expect to see a proposed resolution on the agenda to the effect that the OC is to enter into a contract with X for $Y to carry out the building works set out in the specifications attached to the notice of meeting.
Clause 6 of Schedule 3 of the Strata Schemes Management Act states that for a strata scheme that is not large, where an EC meeting is to be held, at least 72 hours notice must be given to all EC members and owners. The notice must specify the time and place of the meeting and give a detailed agenda. (similar provisions apply to large schemes)
As a matter of general law, where notice has not been given of a proposed resolution/decision, it can be invalid. Clause 11 of Schedule 3 provides that where notice is given by one or more owners whose entitlements comprise more than one third of entitlements, that they oppose a proposed decision, then that decision has no force or effect.
Given what Clause 11 says, if notice hasn’t been given of a proposed resolution, then the owners haven’t been given the chance to oppose it. That might be a moot point in your case, as the investor owners seem to have a majority, but still…
As a general observation, it seems that the governance of your EC is appalling. I suggest you contact Fair Trading. You could also write to the strata manager pointing out the provisions of Schedule 3 and asking them why the EC isn’t complying with them.