
Hi there, Lawrence! This is Marc. Thanks for providing those details. Based on what you've described, here are a few approaches we can try.
To keep things separate, each person should use their own Microsoft account under the Family plan. You can check this by going to Settings > Accounts > Email & accounts on your PC, and making sure your personal Microsoft account (not a shared one) is signed in.
Once you're both using your own accounts, make sure OneDrive is only syncing files from your personal folders. You can adjust OneDrive settings by right-clicking the cloud icon in the system tray and choosing Settings > Account > Choose folders.
Let me know how it goes.
Best regards,