Send birthday wishes to two people (a couple) with the same email address

Good day,

I have some clients who are a couple and I wish to send them a separate birthday wish but they have the same email address as part of my contacts.  How can I separate their birthdate while being on the same contact?  If I were to create two separate contacts with the same email address, I would run into the same problem.  I tried creating a custom field but I am not really sure how to convert it APK  into a separate line item.

Example:  they also have two separate birthdays but they have the same email address.  If I send a birthday wish to Alain, I also want to send a birthday wish to Marjorie as well, but the same email address prevents me.

Can you help.

Thanks