Aside from the issues mentioned above, the "stateroom" would receive the benefits of the gold status. That does not pertain to the individual. Last cruise was WBPC and my wife was Gold and I was Silver (now Gold). I was able to do the online checkin at the gold time and pick Palo and everything else during the window for gold. This is true for everyone in the cabin. The gift received is for the cabin and it will be based on the individual with the highest level in the cabin.
However, I received a sliver lanyard and did not receive any of the other benefits of a Gold member (no invitation to the reception, no discounts in the shops).
The other caveats regarding pictures, being a minor, etc. are all true. Even if the cabins are linked (and you definitely want to be sure the reservations are linked).
One the last sea day of our WBPC there was a lady in Shutters who wanted to get pictures of her daughter who was in another cabin that was linked. The only way to do that is to purchase individual pictures OR if both cabins purchased the most expensive Premium package. Shutters will give you 50% off that package for the second cabin when the reservations are linked.
As for swapping people around if people back out, I can't really say how that works. Changes to reservations get tricky once you reach PIF, but I think you can change things up a bit before that time, as long as you are not increasing the total number of people in the cabin. If you are adding someone to your cabin, it is subject to ship availability. I've heard cases where someone staying in a room that sleeps four wanted to add a fourth person but were denied, because there are other factors than just the cabin capacity that
DCL takes into consideration. Things like capacity at a given muster station, total capacity of the ship, dining rotations, etc.
I understand the concerns, especially with respect to booking onboard activities and shore excursions. Good luck with your decision.