You could do some research on whether it is better to have a single input (B212, B412) or multiple inputs (the rest).
Each one has advantages - B212 with the combining gearbox drives one shaft into the main txmsn, making it fairly simple. But a driveshaft failure means you have lost both engines instead of just one (has happened).
Multiple inputs give more load pathways for redundancy, but increase the complexity of the gearbox.