I'd be glad to help and share some information regarding linking multiple bank accounts in QuickBooks Online, savita-clearnexu.

To rectify the carrying opening balance under the new bank account, you can edit Opening Balance Equity from the Chart of Accounts. Here's how:

1. Click Accounting in the left panel, and choose Chart of Accounts.
2. Find the new bank account and select View register from the Action column.
   
3. Search your register for an opening balance. It should have Opening Balance Equity in the Payee/Account column and Opening Balance in the Memo column.
4. You can enter and change the opening balance from there.
   

However, if there's no opening balance, you can delete it to rectify the amount. On another hand, before setting up additional 2 bank accounts, check with your bank first and see how they send the downloaded transactions.

If the statements are downloaded to one account, connect only the parent account. If they are imported to the individual accounts, you can add the 2 as sub-accounts under the parent account and link them. Here's how to add a sub-account:

1. Click Accounting in the left panel and choose Chart of Accounts.
2. From the Chart of Accounts screen, click New.
   
3. Choose the Account and Detail Type.
4. Enter the name of the account in the Name field.
5. Mark the box for Is sub-account.
   
6. Click on Save and Close.

To learn more about setting up parent, sub-accounts and connecting them into online banking, see the recommended articles below:

About bank or credit card subaccount setup.

Create subaccounts in your chart of accounts in QuickBooks Online.

If there's anything else that I can help you find in QuickBooks Online, leave a comment below. I'd be happy to assist you further. Wishing you the best.