There is not (yet) an easy solution to use an an iPhoto library with two separate My Photo streams.
It might be easier to take the family photo library out of your wife's account and move it to a shared location, so boh of you can maintain it, see:
This way, both of you could download automatically to My Photo Straem and your private iPhoto Libary, remove the worst pictures, and then export only the best shots to the shared library. This will make the shared library smaller and at the same time create a backup of the best pictures, and it will ensure that your family will never see a potentially embarrassing photo. Sharing My Photo Stream is really dangerous, because each and any picture you take will be added the PhotoStream, before you can delete it.
As you may have seen at Apple's WWDC keynote presentation the new MacOS X Maverick will bring more sharing options for Photo Streams: Watch the keynote
You may want to wait for the next software generation before doing any major reorgansition.