Zosia has a question about Windows 10. “Can I upgrade to 10 on my PC and keep 7 on my laptop?”
Zosia, your computers aren’t connected in that fashion. They’re independent, separate devices. You can choose to upgrade either one of them without affecting the other. Each of your PCs has a separate license for Windows and you can choose to upgrade one or both of them without affecting the other.
And don’t worry, you can continue to use the same Microsoft ID for both PCs.