You will need to add the spouse as a LINKED contact to the primary contact.
Go into Contacts and find the primary contact.
Click Preview next to their name
In the pop-out click on Add a Linked Contact.
Fill in the form with the name, relationship, and birthday.
Then submit
Note: the address for the primary will pull over into the new linked contact
NEXT
The Linked contact will now have their own contact record
Search for their name in Contacts
Check the box next to their name and click on ADD TO GROUP at the top.
From the drop-down menu select the group enrolled in the Automation you want to add them to
Read the pop-up and follow instructions