You will first need to do a FindManagedObject using the name of your group in the params. Eg
send FindManagedObject(reqId, "", { "query":"name eq ' EPL_Event_Check_Group'"}) to FindManagedObject.SEND_CHANNEL;
In the response you will have all the child devices or child assets and their related Ids.
From there, you simply create your listeners based on those Ids.
An example would be:
on all Event(source=One_of_the_Child_Id_received, type = Constants.INPUT_EVENT_TYPE)
Yes indeed, and keep in memory the ids of the device you already created a listener for. So you dont recreate the same listener for the same child devices when you receive an update of the MO Group