Calls from my wifes 5s show up in the recents list (as well as my calls) on my iphone 6. Calls from my phone show up with her calls on her phone as well. Any idea why this may be happening?
We do share the same apple id.
Since both iPhones are using the same Apple ID they're probably using Continuity. This is a feature introduced with iOS 8 that enables calls made to one device to be answered on another device. Your example is the part of Continuity called Handoff. Use Continuity to connect your iPhone, iPad, iPod touch, and Mac - Apple Support
To turn it off, go to Settings>Phone>Calls on Other Devices and select which devices you want to receive your phone calls.