Each company file requires its own paid subscription, James.
Having two QuickBooks Online Plus subscriptions will not affect the account service of the other since each subscription is separate.
On the other hand, you can have multiple companies in one QuickBooks account by purchasing the subscription and using the same login credentials. You can switch between companies by going to the Gear icon and clicking Switch company.
Additionally, you can refer to this article about modifying your company information: Change your company name, contact info, or ABN in QuickBooks Online.
I'm always here to help if you have other questions about your QuickBooks companies. Take care.
