I have a checking account in which I am only responsible for half of the income and expenses. How can I reflect this when entering transactions from the banking page?

Hello there, @fordfarmsbeef.

When recording transactions on the banking page of QuickBooks Online, you'll have to enter the amount which you are responsible for in the checking account.

To add the transaction, please take these steps below:

1. Go to the Banking menu at the left pane.
2. Refer to the Banking tab.
3. Select the entry that needs to be added to expand the view. 
4. Review the recommended account category. This is the account QuickBooks wants to categorize the transaction into, and make changes to the payee and category before you hit Add.
5. When everything looks good, press on Add to record the transaction.

I also recommend excluding the transactions that are not part of income and expenses to keep you records accurate. Please see this link for reference: Exclude transactions in QBO. 

To learn more about adding bank transactions in QuickBooks Online, please refer to this link: Download, match, and categorize your bank transactions in QuickBooks Online.

You can always find me here if you have any other concerns. It'd be my pleasure to help. Have a wonderful day!