I believe they have ditched the 2/3 rule a long time ago and nowadays the decisions have to be unanimous. I don't remember which video it was but some elder who had been at Bethel had talked with a GB member and got the impression that all the members have to agree. I will try if I can find that video.
This info about 2/3 majority is based of Ray Franz's book. He left in 1980 and many things have changed since then.