Hi All, Anyone done a Grouped invoice via code? (2 or more Sales orders into 1 invoice for the same customer)

I am not sure why you want to create 1 invoice for multiple sales order. Or what is the business requirement. But you can have a custom field on the invoice body or and in the sublist line that tags each sales order. Ideally what some of the business wants is instead of sending multiple invoices to the customer, send only one. So it will be easier for you to generate the pdf of the invoices in grouped form.

I know you can do grouped invoices via the UI. So customer wants to recreate the same via script

Provide a suitelet. Where users can select the customer. Based on the customer selected all the invoices should come in the sublist of the suitelet.. They click one checkbox against each invoice they want to group. Click on a button which calls another suitelet that generates the pdf. You can use advanced pdf or write html code in suitelet itself to create the pdf format. How the invoice will look will depend upon the needs. But you can build something like this.