If you want to add multiple contacts who share the same email address, you can try the following approaches:
For Gmail users
When adding the first contact, enter the shared email address. For the second contact, enter the shared address but add a plus sign and some identifier before the domain name. For example, if the shared address is firstname.lastname@example.org, you might enter something like email@example.com. Email systems like Gmail ignore anything after the plus sign, effectively making these two emails the same.
For Hotmail users
Systems like Hotmail allow users to create alias addresses. After your contacts have created their aliases, you can use the aliases as different email addresses within their Wild Apricot contact records.