Yes, you can put multiple modules on the same channel. Multiple modules on the same channel will fire at the same time.
Using multiple modules on the same channel does introduce some challenges with checking continuity remotely via the controller. For information on that please see why does the continuity LED light blink green on my 18R2?
If you are scripting your show, we recommend keeping all modules on different channels as this makes setup and reporting on signal, continuity, and battery levels much simpler.