Prior to Parallels Version 11 you were able to use the Parallels software on any of the Macs you owned and used for non-commercial work. With Version 11 you are no longer allowed to do this. So you need to purchase a license key for each and every Mac.
VMWare Fusion has a completely different policy that states the following:
Can I use a single license on more than one Mac?
VMware Fusion for personal use:
You may install and use VMware Fusion for personal, non-commercial use on any Apple-branded products running Mac OS X (“Mac Computer”) that you own or control.
– See more at: https://www.vmware.com/support/fusion/faq/licensing.html#sthash.Y452Lrq1.dpuf
I’m going to ask Parallels for a refund and make the move to VMWare Fusion. Don’t get me started on Parallels annoying pop-up dialogs.