[mothered]

so since I am using another person's account email, should I just act a though I am them?  

From an account standpoint, you'd want to simplify It as best as possible.

A device Is not required to register an account, so why not create your own Fitbit account?

Yes but the devices linked to the accounts are under warranty, and you can't setup the devices without an account.  I guess I could try, but it seems like it would be much harder.

Your elaboration has helped understand exactly where you're at.

If you're going to use another user's email account and given It's registered with their details, you'll have to assume their role. Conflicting Information may trigger alarm bells.