You can add multiple people to a contact by creating a company. This will allow you to add as many individuals as required to your contact.
Please watch this video or follow the steps below:
1) Create a new contact, and select "Add a company".
2) Fill out the details for your primary contact.
3) Click on "Add another contact to this company" to add additional contacts.
What can I do with company contacts?
1) Add your contacts from a company onto your document templates.
2) Changing your invoices to be addressed to a secondary contact.