Brother hardly has any friends?

K so im 15 and have a twin bro with cerebral palsy. He doesn't have it to bad so he can still walk talk and act normal. Well this hasnt really hasn't happened since we got to highschool. But he doesn't have many friends.. And it's not that no one likes him, he is just really shy. Our neighbor used to be his best friend and hang with him all the time! Now that we are older he wants to go out places. He doesn't invite my bro to hang as much. But he is nice to him. So during the summer I swear all he has done is like played playstation watched tv or hung out with my fam. I can't tell if it's bothering him or not. I think he is mostly shy because he has low self-confidence. How can I get him to be more social? How can I stop feeling bad for him? :( :( also I have invited him to some stuff when I hang with my guy friends but I can't ask him all the time! I have my own life too. I just can't stop feeling bad for him! :( :(