End of R & G

This act begins with Rosencrantz and Guildenstern waking up on a boat on the ocean. There is a big umbrella turned over and three barrels. Later, Ros and Guil look at the letter Claudius gave them and it says to have Hamlet executed. They then go to sleep as Hamlet blows out the lantern. Next, the audience sees that Hamlet replaces the letter Claudius gave them with a new one.
I have a hard time understanding what happens next. I understand that pirates come and raid the ship and then the lights dim. When the lights come back on, its just the tragedians and Ros and Guil left on stage. Ros and Guil look at the letter again and see it has been replaced and now says to have them killed instead of Hamlet. Then, I think that the tragedians betray the two guys and then they start talking about death. Guil grabs a knife and stabs the tragedian. It then turns out that it was a fake knife and then Ros calls for another performance. From then on, I am really confused. All I know is that at the end of the act, the audience is shown the corpses of Claudius, Gertrude, Hamlet, and Laertes. I have no clue what to think about this.