Is there a way to see all the invoices sent to my billing customers?

Sure, there a multiple ways to see the invoices sent to your billing customers. 

1. The Invoices tab in Billing will show you all of the subscription invoices that have been sent to your billing customers.
   
2. You can also see the subscription invoices under Invoices. However, subscription invoices are excluded from this view by default and the store owner can remove the exclusion in the Display settings panel. 
3. You can also see the Invoices under the subscription for a single customer by selecting the Invoices folder tab. 
4. Finally, you can see the invoices under a Customer by selecting the Invoices folder tab. Unpaid subscription invoices will also display in the Unpaid folder tab.