I need to set up a customer who displays as "John Doe and Jane Smith" for billing address and invoices. They live at the same address and are one family.How do I do that?

Welcome to the Community, @ianlmcr. I'm here to guide you on setting up a customer's name that displays as John Doe and Jane Smith on your invoices. 

Let's edit your customer's name in the Customer Information window. From there, you can enter their name in the Display name as box. Here's how: 

1. Click the Sales menu, then go to the Customers tab. 
2. Locate and select the customer's name, then click the Edit button. 
3. Enter John Doe and Jane Smith in the Display name as box.
4. Enter the Billing address. 
5. Click Save when done. 

Here's a screenshot for your visual guide: 

And this is how it would look like when you create an invoice:

Here's an article for your reference: Manage your customer list. It also includes steps on how to delete, merge, and add sub-customers in QuickBooks Online.  

Let me know if you have additional questions. We're always delighted to help.