Hi Jane,
I hope you are doing well.
1, For your first question Is the action 'Send an Email' going to wail till all 3 parallel actions finish/complete and then execute?
The answer is Yes
You can have two or more parallel actions that run simultaneously, after which the next action will only proceed once all parallel steps have been completed.
2, For your second question how about one parallel action fails, will the action 'Send an email' stop?
I test it in my sandbox environment, I found that if any parallel action failed, the next step will be stopped.
Please refer to the below test run.
If this helped you, I'd appreciate it if you'd mark this as a Verified Answer, which may in turn help others as well.
Thanks.
