The most worrying thing in this is this line: “OC is not willing to bear any liabilities and costs involved. What should OC do to avoid them?”
There are no Strata Kops. Fair Trading is not going to come around and solve this for you.
Actually, Fair Trading isn’t going to do very much at all.
The OC has responsibilities and if they cost money, tough. One of those responsibilities is to look after the fabric of the building. If that means you have to hire a lawyer or consultant or surveyor or whatever to prevent selfish owners from doing whatever they want to the building, then that is what you have to do.
That said, follow Lady P’s advice above and start by ringing the council. Doing nothing is not an option … you will end up paying for it in the long run.