Manage multiple Monthly 4G lines from a single My T-Mobile account

I have a new Monthly 4G account and I can't seem to find any way to add the new account to my existing "My T-Mobile" account..

Also I have an existing Pay as you go plan on another "My T-Mobile" account/login.

So I really have 3 distinct questions. Is there a way to:

1. Add a new Monthly 4G account/phone number to my existing My T-Mobile account?
2. Combine an existing "My T-Mobile" account managing a pay as you go phone to my newly created "My T-mobile" account?
3. If all three accounts were consolidated, would there be a way to refill each account separately or would funds be deducted as needed?

Thanks,

Peter