As Jimmy has said, it doesn’t matter how many people decide something, if it is illegal or contravenes legislation, or even in some cases cuts across someone’s rights then it can’t/shouldn’t proceed.
The other owners could resolve to remove my front door – that doesn’t mean they can actually remove my front door.
1. Threshold question – is the balcony common property or is it on the owner’s title? If it is not common property then the OC should not be paying for it at all, and you have a good case for seeking an order to stop it.
2. If the balcony were common property and an owner was seeking compensation for purported loss or costs incurred due to works, the owner would have to quantify that loss, or provide evidence of those costs. If the owner were to claim for loss/reduction of rent, they would have to provide evidence of that, e.g. agreement with the tenants, in writing. It is then up to the OC to determine whether they believe it is appropriate to pay the owner anything.
The reduction would also have to be reasonable taking into account a range of factors including the size of the balcony relative to the apartment and the inconvenience (if any) to the tenants.
If an OC is responsible for carrying out repairs they have full control of those works, including any investigation and obtaining reports etc., following through to determining scope of works etc. If it is the OC’s money then it should not rely on reports of the owner. Note that the OC has the right to enter the premises to carry out repairs.