If you're the admin of the group, it's really easy. Head to the 'Group Settings' and tap on 'Disable messages for all except admin' to disable the message sending function for all group participants. You can turn it back on by following the same steps. 😎
PS: Only the group admin can share messages in the group, if 'Disable Messages" for all is off.
The group members will see a message saying 'Group Admin has disabled message sending for other participants'