Hello Dino
As it happens, I've got twin boys too (and wrote a book on twins - guess who inspired that?). I have learned from experience that twins don't always do the same things at the same time, or develop at the same rate. If they weren't twins, but, say, two children the same age who are cousins, then you probably wouldn't have posted this question at all.
It's only been a few weeks since the other twin became dry, and there's no rush, so don't worry. My advice is to leave it to your son. Don't scold, don't bribe. He knows he has a potty to hand (it has to be his own, not shared), and he knows what it's for. Eventually, he'll use it. If, come the summer, he still shows no desire to use a potty, then you can leave him with his nappy off, perhaps out of doors, and see what happens. I'm sure he'll become both clean and dry before you know it.
Good luck and have fun with your boys.
