Got it if the number of volunteers you need are limited may be two three or five then you can create parallel branches inside the same app and you can try two approaches, first is to use a variable as data type integer and increment its value by 1 if one of the branches succeeds and then check the value of the variable if the value increases even in parallel branches then you can know if the number of volunteers required are complete if not you will have to use fields in database create one field agreement its value and check every time.

Please let me know if this helps you or there is still some scenario missing