The scenario is straightforward.
If the Home windows was a retail model when bought then it’s transferable to a different machine supplied it’s deleted from the unique machine.
If the Home windows model is OEM ie provided with the unique machine by the producer then it’s not transferable and is tied to that particular machine and can’t be transferred.
So if your folks Home windows is retail he can do what he’s intending if not he cannot.
Identical for you. In case your Home windows was retail you’ll be able to switch it however whether it is OEM you’ll be able to’t.
Having stated you can acquire new licenses from a number of sources that are less expensive than shopping for from MS. Take a look opn eBay/Amazon however watch out as a number of affords there are usually not real. There’s a moderately good supply obtainable from the Journal “Pc Energetic” and these are real.