These are three person ski's but 3 full size adults will make the machine top heavy and more likely to tip over. We rent 3 person machines so that both parents can take a child out and have enough room for all, not for 3 adults to use. For you safety and enjoyment their is a 400lb wieght limit for rentals.
Climbing back on the ski after you fall off is a lot harder than you think. Just about no one falls off if they try not to.
Stay away from seaweed floating on the surface. It clogs up the intake and slows the ski down. If all of a sudden the ski is not going fast and there are no other obvious signs as to why, this is probably the problem. FYI, there is much less seaweed in Cape Cod Bay (where Dennis Parasail is) than in Nantucket Sound (where every other jet ski rental company is).