My twins are a similar age, and their favourite game a few months ago was to wait until my back was turned and destroy their brothers' carefully built lego ships. It was very frustrating, I had to watch them every second. In the end I bought a lock and put it on the outside of the older boys' bedroom door, so I can lock them out. Is there a room you could put anything you don't want him touching it and lock him out until he gets over this? I promise this phase will end but I know how tiring it is