Adobe allows you to have the same purchased activated serial number on no more than two of your computers. And, you do not run the two at the same time.
So, if you had Premiere Elements 11 activated serial number aaaa bbbb cccc dddd eeee ffff on each of your old laptop and PC, you could not use that same serial number on a 3rd computer.
What are these two older versions of Elements - what version and what operating system?
What are you considering - Premiere Elements 13 - and then Windows or Mac?
If you are buying a new license with installation files (with its unique new serial number) for a new laptop and a new PC, I am not seeing an issue.
Please review and consider and then let us know if you have questions or need clarification.
This is not Adobe. Rather user to user.