how to stop cPanel backup during the process?

The only way is to rename your backup Drive to something else and the process will be stopped.

The other way can be unmout backup drive for a short and the process stops.


Other Solutions can be:

kill the children....so do I go to TOP, then search for the PID and then...KILL?

**kill childrent not homocide**

Yes. All you can 

ps -aux | grep pkgacct

and kill the process ID that comes up