It’s going to be a family affair this fall when Julie Andrews directs a new musical, “The Great American Mousical,” based on the 2006 children’s book the actress wrote with her daughter, Emma Walton Hamilton.The show will receive a workshop production Nov. 8-Dec. 2 at Goodspeed Musical’s Norma Terris Theatre in Chester, Conn. Tony Walton — Hamilton’s father, Andrews’ former husband and the illustrator of the book — will design sets and costumes for the musical. Writer-performer Hunter Bell (“[title of show],” “Silence! The Musical”) will write the script with music by Zina Goldrich and lyrics by Marcy Heisler. Christopher Gatelli choreographs. The book centers on a troupe of musical-making mice living in a theater threatened by demolition. At the Goodspeed Opera House, Andrews previously staged a 2005 revival of the musical “The Boy Friend,” a production that then toured during the 2005-06 season. Walton helmed and designed “Where’s Charley?” at the theater.