What should i do for my crippled puppy?

My dog had pups in Feb of this year. We found out that she had sat on him or something because he was a late walker. We had taken him to the vet and he gave him a steroid shot making his walking better. Now he walks frustrated and twirls trying to get to his destination. Recently his brain has been growing out of his skull ( so says my mother) we're convinced that another shot wont work (seeing as he's gotten worse) he can't stand and every time i lean him against the wall for water he seems to drink alot. Should we risk another shot that might not work or go ahead and put him down. We only open that last option because he wines when he cant get some where and gets tired very easily. HE can't get down from the carport ( or doesn't try to) to go to the bath room like his mother and sister. I have a light chance of hope when he comes bolting fomr the carport and trys to take a toy from his sister. He gets stepped or and on by his sisters and its hard for him to play or get the basic needs.