Let's say you want the bride and the groom to have a quote/ invoice.
First, add whoever will be signing & paying for the quote as the contact (so that their name shows on the quotes and invoices).
Next, click 'Send to Client'

From the pop-up window you will be able to add in multiple email addresses separated by a comma.

This is where you can enter in another or multiple email addresses and they all will have the ability to sign and pay. 

Note: They will not be separate contracts so once one of them signs and/or pays, it will show up as signed and/or paid for both.  Also, the name on the contract will be for whoever is assigned as the client. (E.g. If the bride is the contact, then it will say her name).