I've seen the same question asked in other forums, and people have said that RCCI is pretty adamant about not opening the balconies between cabins. Once you get on the ship, you'll see that it wouldn't be as easy as unlocking a door.
You can certainly have a conversation over the railing, and you will absolutely be able to hear every word that they are saying when they are on the balcony. But if you don't have adjoining rooms, you won't hear conversations (or other noises) when you're in the rooms. That's probably a good thing!
If you're like most people, you'll spend virtually no time in your cabins. You'll be out on an excursion, on the pool deck, in a restaurant, or at a bar.
Have a great time!