1. Team one, come up here. Are you ready? Go!

2. Team one, come to the front. Who is the movie director? You should say, "Ready? Let's go." Then act in the play.

3. Come up here, members of Team 1. The director should say,"Ready? Action!" Then you should start acting out the play.

4. Team 1 should start acting in this play. The director in this team should say,"Ready? Action!" Then they can act out.

[Which ones are correct and commonly used? Would you correct any errors? Thank you.]

As I have explained before, numerals under 13 must always be spelled. It's Team One, NOT Team 1 when used in a sentence.

#1 is fine.
#2 "then act in the play" is a phrase, a prepositional phrase, not a separate sentence.
#3 is fine
#4 Same as #2

1. Team one, come up here. Are you ready? Go!

This sentence is correct and commonly used. It is a command or instruction for Team one to come to the front and start their performance.

2. Team one, come to the front. Who is the movie director? You should say, "Ready? Let's go." Then act in the play.
This sentence is incorrect. The question asks who the movie director is, which is unrelated to the instruction for Team one to say "Ready? Let's go" and act in the play. To correct it, you could rephrase it as follows: "Team one, come to the front. Are you ready? Let's go. Then act in the play."

3. Come up here, members of Team 1. The director should say,"Ready? Action!" Then you should start acting out the play.
This sentence is correct and commonly used. It instructs the members of Team 1 to come to the front and for the director to say "Ready? Action!" to prompt them to start acting in the play.

4. Team 1 should start acting in this play. The director in this team should say, "Ready? Action!" Then they can act out.
This sentence is correct and commonly used. It provides a clear instruction for Team 1 to start acting in the play after the director says "Ready? Action!"