I have 3 weeks twin boys. one twin i think there might be something wrong with his because he is always opening closing it as if he is shivering. should i be worried?

Congratulations!: You know infants are not very good with staying warm. Please make sure you put enough clothing on your twins. Your question is not as clear as you think. What is your boy opening and closing? Shivering is just a way for people to stay warm so make sure that the infant is warm if shivering or check temperature to make sure there is no fever. They also get startled easily do not worry.