It should work if you do the following.
1- both phones need to have software version 5.0 or higher.
2- both phones have to have iCloud Calendar option activated.
3-both phones must use the same Apple ID when activating ICloud.
Thank you for the welcome and replies. I think we figured it out. It turns out the my wife has Microsoft exchange synced to her work email, so I had to add her work exchange to my phone. It seems to be working fine now.