I understand the importance of managing common names of clients and companies you provide service to, Titan. I'll provide another workaround to manage your customers in QuickBooks Online.

Since you don't want to enter the middle name of your customer, you can use another identifier, like numbers and letters in the Customer Display name field. By doing so, you can differentiate customers even if they have similar names. You may refer to the image below:

In addition, you can customize the template so the identifier you enter to their name won't show in the invoice when your customer receives it. To start, you can edit or create a new invoice template by following these outline steps:

1. Go to the Gear icon, then select Custom form styles.
2. Select Standard, then click Edit if you like to customize the default template. If you want a new one, click the New Style button, then select Invoice.
3. In the Content tab, select the header and information display or the upper box.
4. Untick the box for the Form names in the Forms section.
5. Click Done.
    

Afterward, create an invoice, then select the invoice template in the Other Templates (view only) section of the Design menu. Once done, click Review and Send. You can also remove the identifier on the customer message before sending it to them.

Furthermore, I'll attach this helpful article to guide you in managing your customers within the program: Add and manage customers in QuickBooks Online.

To learn more about making changes to your invoice templates, check out this article: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Also, you can record your customers’ payments once they’ve decided to pay their invoices to keep your records balanced and accurate.

Please stay in touch if you need further assistance managing your customers and other QuickBooks-related concerns. I’m always glad to help in any way I can. Take care and have a great day!