Sounds like a lose / lose situation. If you go, you will rig, row, derig, set camp and generally be working the entire time, while his "Family" gets to enjoy having a vacation. If you turn it down, you lose out on the trip. Try to make him see it as win / win. Be honest with him about you questions as to him and his families experience and lack of gear.
Claimer: Someone that makes a claim that they have been there and done that, can do anything you can do better than you. I hate "claimers"