Yes, all the three passengers can board the train with this ticket. Connect with the TTE at the station or as soon as you board and request him to allocate 2 berths to you whenever available. You may be allocated a berth from the boarding station itself if you are lucky. You don't need to pay anything extra (if allocated in the same class) for this. If the berths are not available, you just have to adjust 3 passengers on one berth which is confirmed.