Many people have Windows 10 on multiple devices. Yes you can install W10 on every qualified computer you own.
About Pro Edition... See the upgrade path to determine what Edition each machine will upgrade to.
From:
https://forums.windowscentral.com/e...ws%2Fwindows-10-specifications&token=ulM-cTRh
This is the upgrade path for the free upgrade offer which is expiring July 29th, 2016. If your free upgrade would deliver Windows 10 Home instead and you want Pro... You would have to purchase Pro as a disk or as an in place upgrade after install of the free upgrade. Purchase would give you a license for one device. Purchase as many licenses as you need (from 0 - 2).
About turning one computer off to use another... Not sure what you are after here. Is it worrying about having two computers on the same Microsoft Account?
You can have 2 computers on the same Microsoft Account. You can even sync settings between them or turn sync off for devices on the same account.
More details about what you are trying to accomplish, or what you wish to avoid would be helpful in getting a more detailed answer.
If your desire is to make one Pro purchase and split the license between two devices that won't happen. Your license will be specific to one unique set of hardware that makes up the device and even if every component were the same it still won't "spoof" the system into thinking they both are just one computer.
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