I appreciate you for being specific on what you need to achieve, @sarahlizzy4.
It's good to know you're using the Class Tracking feature in QuickBooks Online (QBO) to track each property as a Class. You also have the option to assign expenses to a specific class/property to have visibility for both earnings and expenses that you're incurring for each property. Then, pull up Profit & Loss By Class all the time.
These would be your Customer hierarchy for any QuickBooks for rentals:
Customer is the property
Customer: The customer is the actual apartment
Tenants: Customer: The customer is the tenant
Once you've set up the tenants as customers, record the rent income as invoices when you receive payments at a later date. Otherwise, creating sales receipts is appropriate when you receive their payments instantly.
For more details, check out this article link: Set up Rental property in QuickBooks Online.
Here's an article that will guide you through recording transactions for a property management company.
Feel free to visit the Community again for your additional concerns. Have a great day!