There are videos on YouTube of people out with two people on AI's. I've taken my dad out, he was the heaviest person. I'm about 170lbs, he's about 155lbs. The capacity for the Adventure Kayak is 350 lbs. The weight capacity doesn't increase with the Amas on the Adventure Island.
200 lbs of weight can be mounted on either trampoline at a time, but that means that you only have 150 lbs of capacity left. In other words, if you have a 200 pounder on your tramp, you better weigh 150 or less.
Having said all of that, the AI can definitely sail with two people. The boat will sit lower in the water, and be slower. In our case, we felt the most comfortable switching sides with each tack to put the person on the trampoline on the high side trampoline.
The lighter your total weight (two people, plus gear) the better it is. It's wet, and the second person can't expect a plush sailboat ride. It's wet, but fun. Not fun in the adrenaline rush way, just fun in the, "We're out on the water in a tiny little boat, one with nature" kind of way.
So yeah. If the weight works, and you're not planning long trips, and your passenger is aware of what it means to sail with two people on a single seat Adventure Island, Go for it!!