You have two options:
One by one: the numbers are called one by one in the order you set. We try to reach each phone number for the duration of the set ring time (default 25 seconds). Then the call continues to the next phone number in line.
Simultaneously: with this option, all numbers are called simultaneously for the duration of the set ring time (default 25 seconds).
You can adjust the ring time for each virtual number under Forwarding in My Rinkel. And you can use the No answer settings to decide what should happen when the call is not answered.