It was totally irresponsible to put that kind of weight in a 21 ft boat, let alone in that weather. My husband was saying that the four of them could weigh close to a thousand pounds.
The boat is rated for more than 1000 pounds. See the link further up in this thread.
But it’s designed for travel in lesser seas.
I would think they each probably weighed 250, that would be 1000 and I would think that would be a minimum and wouldn't take into account any gear that they took along, food, water, etc.