Volleyball drill: service pass exercise

Service pass training for 4 to 12 persons
4 persons:
2 servers on the service spot .
1 passer
1 catcher
(static) Server serves, passer passes the ball to catcher, catcher catches the ball and rolls it back to the server.
(dynamic) same as static, but then the involved player walks after the ball. (server becomes passer, passer becomes catcher, etc.)

6 persons.
2 servers
3 passers
1 catcher
(Static) see four persons
(dynamic) server serves the ball and walks after his/her ball.
Passer passes the ball to catcher. The most right player becomes catcher
Server moves in from the left. Catcher becomes server. If this does not work, 1 passer becomes reserve.