Unfortunately you have to terminate the tasks in the other parallel branches to end them. If your workflow completes after your parallel eventually task will terminate cause workflow ended but it takes like 15 minutes on average after workflow completes. 

I find terminating specific tasks in one instance a pain in the butt so good luck. I'm curious if Nintex plans on updating the parallel action to better support tasks in branches when completion condition set to true.... in theory tasks on other branches should auto terminate by the system when this is set to true.

And triggering all tasks independently in component workflow is not ideal cause you cant gather all custom task form controls by using nintex workflow actions for tasks so keeping them in one onstsnce is critical unless you plan on keeping track of every detail of tasks in a list or other source outside the system. 

@brandiwoodson. Thanks for the quick reply. I am very new to Nintex so I am not sure how to terminate the task that is running. I still want the workflow to go to a different path when it is rejected and another path when it is approved. So I don’t really want my workflow to end yet. Do you know if there is any sample that I can have a look? Thanks.

Its more complicated than it should be. They don't have an option to "terminate" a task. 

You'd have to use complete a task action which falsely completes it and what you have to do will depend on your business requirements and what you need.…what do you need from task form controls?

Your best bet is to setup one task...send it to everyone in task assignee field and do first response behavior vs using parallel and multiple tasks.

Help documentation for complete a task

https://help.nintex.com/en-us/nwc/Content/Designer/Actions/NintexWorkflowCloud-CompleteATask.htm

Here is help documentation on assign a task to multiple users. Outlines the completion rules...use first response

https://help.nintex.com/en-us/nwc/content/Designer/Actions/AssignaTasktoMultipleUsers.htm