Multiple companies with different tax identification numbers (TIN) will each have their own QuickBooks Online subscription set up. This is in compliance with IRS Pub 583, Page 5 wherein you need to keep separate books per company.
You need not worry, you can use the same login credentials for all the 7 companies when signing up and switching between Companies.
1. Go to https://quickbooks.intuit.com/online/. 2. Choose a version of QuickBooks. 3. On the signup page, select Sign in. 4. Enter your login information and follow the on-screen prompts to set up the second company. 5. And then to log-in to your account: http://qbo.intuit.com. You will have the option to select your companies.
Once signed in, you can go ahead and click the Gear icon at the top to Switch Company. For more information, you can refer to these articles:
If you are reluctant to open 7-8 QBO accounts separately, you may consider using QuickBooks Desktop instead and deploy a private cloud to let users working on any file with LAN and internet connection concurrently. Just my 2 cents