At home I have 3 PC's , all 3 individually upgraded from windows7 SP1 to Windows10 Pro, and automatically activated without any problems. The funny thing is that all 3 have got the same Key. Is that normal?
Those are generic keys for the Pro SKU. Your new key is your HWID (hardware id) that is unique to every computer. Should you ever reinstall Windows on those computers, just skip any prompts to enter a product key, go online and you'll automatically be activated.