They are already adults. They can do whatever they want. So the first thing these cousins did was a stay in a rented apartment and, when they were alone there under their own responsibility, the kids did not come up with a better idea than exchanging the brothers. Since they were young they fantasized about doing that, fucking cousins in a family orgy and seeing how they enjoyed sex. The kids also wanted to do it but they let their brothers take control of the situation and it was they who took the first step. They had a great time!