Ok, this is weird. I did what you suggested, and it brought up my wife's contact details correctly.
When I say "call my wife", Siri replies with:
I don't have a wife number for "me". Would you like to use "my number" instead.
But if tell Siri to "call my wife's iPhone", it works as it should!
You might have a random contact place in your address book messing things up that you accidentally added