I am a Padi and Naui instructor and have taught for nearly twenty years total, which just reminds me I am getting old, but anyway, I teach all of my courses as privates, or small groups that know each other already. I always allow family members to attend pool sessions, classroom whatever they like. It makes some people feel more comfortable having a family member around, alot of time, they are here on vacation and the "family" member doesn't really have anything to do while they wait.
If the family member is going to dive with us, which is something I encourage, I'll ask them how long has it been since you dove? If it's some length of time, or maybe they've got a bunch of new gear, I'll bring a tank and let them swim around too. What the heck I am there anyway, and...if they need a little tune up, or something fixed, I'll know before I jump off the boat with my student. I have had some dive along family members cause me more grief in the water than the student, so I just kind of work with everyone in a relaxed freindly manner. Ultimately, for me it's about my student having a good time, learning what they need to learn, and if that means taking on a family member great. If that is the "dive buddy" my student is going to have once he/she is finished with their class, I like to see how they are going to work together once they are long gone out of my sight, and most of the time it's very enjoyable for everyone, myself included.
With that being said though...I don't take crap from anyone, if you interrupt me while I am trying to work with the student, slow things down to much, argue with me, or just be disruptive in anyway..I'll tell the family member to do one of two things. 1. Let me earn the money they are paying me and let ME to the teaching, or they can start over with a new instructor.
I rarely ever have a problem, and I teach hundreds of kids, I tell the parents that I encourage them to all come do the check out dives together, but to remember...let me teach, and then I joke with them...hey your paying me right!
Well just my thoughts...if you and your wife get along great, I wouldn't see a problem, just remember be supportive, don't be over critical of her skills in the beginning, and things will be great! Good luck and if you ever make it to Palm Beach, come dive with us..both of you!