If you do not already have one, you need to make a contact for yourself in Contacts.
When you edit that contact, one of the options is to Add Field (it is way down at the bottom just above the Delete Contact button.
When you click Add Field, one of the options is to add Related People. You can then add all kinds of relationships...wife, husband, boyfriend, girlfriend, spouse, partner, mother, father, child, friend, assistant, etc.
After you have saved all your info in your contact, go to Settings > General > Siri and make sure that your contact is the one selected under My Info.
This way, when you say to Siri "call my wife", Siri will look at your contact to see who you have saved under the relationship field "wife".