Hello, r-butterworth. I'm here to lend a hand.
Yes, he may use the same login credentials to manage multiple QBO accounts. You can also switch from one company to another. Here's how: How do I switch companies?
For future reference, you can visit our QuickBooks Articles hub to search for relevant topics in managing your account in QuickBooks Online.
As always, the Community team is here to help you. Keep safe!
One QBO account is for one company file. You may manage branches/divisions by utilizing the Class/Location feature available in QBO Plus. Otherwise you should open a new account.
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