USAFRet :
A Win 10 OEM license install is tied to that original motherboard.
You will no have 2 PC's, yours and your parents. You need another OS. That Windows 10 OEM goes with the old motherboard.
Assuming you keep that OS install with that motherboard, it will not need a new install. However....you should. There is a LOT of your info remaining in that install and Registry.
It needs a clean install....and with the same 'system' (motherboard), a reinstall is no issue.
So basically, you are giving them your PC, and building a new PC for you.
This new PC needs its own OS.
For your games? With Steam games, copy the steamapps folder to elsewhere. This you can reuse.
All you other applications will need to be reinstalled on your new PC.
Yup, I already have another Windows 8.1 Key here. I was only worried that I will have to redownload and install all my games again.
So now, I'll probably just move my RAM, Motherboard, Processor, and Hard Drive to my parents pc. Last question, will a Windows Refresh reinstall windows without deleting all those files?