The email address is the unique identifier for a contact, so you can't have 2 contacts with the same email. You can store the second name under a customer field (like Spouse), then you can use a Segment to find these secondary names and send them to a new list or use the Segment to send to the secondary names.
I apologize if our response was not the answer you were looking for! However it’s important to note that if you upload contact A with one email address, then add their spouse as a separate contact with the same email address, contact A’s information will be completely replaced with their spouse’s. As the previous agent mentioned contacts are identified by their email address. So our system will update contact information rather than making a duplicate.