Invoice Grouping for 2 different orders for customers

Summary:

We have a requirement to create invoice for 2 different orders for different customers at the same time.

Content (please ensure you mask any confidential information):

At the time the main Product is shipped out to one customer, the by Product is billed to another customer based on a certain ratio. Both the orders however should be invoiced at the same time. Is there any grouping rule which can be used across sales Orders.

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Code Snippet (add any code snippets that support your topic, if applicable):