That would depend on if you are doing a b2b on one direction and then another the next week.
The entertainers usually don't get on the ship when you do, and travel the whole cruise. They fly into different ports to meet the ship. That is why sometimes you get re routed on your cruise, there is no "headliner"that night in the show room. If this happens, the staff puts on a show, or they come up with something else to do.
There are several ways to do a Back to Back. You can Take the same ship, the same route for two weeks in a row.
You can take the same ship doing Western, then the next week do Eastern
You can go on one ship, one week, and then come back and take a different ship the next week.