Just to add it will be better and cheaper, ( courts and solicitors cost a lot of money) , if the stepfather and mother can get together and with the child find a sensible arrangement between them. At 14 the child is going to have a very good idea as to what he wants, if it went to court the court would almost certainly go along with what the boy wants to happen.
Remember it is always the child who is the most important the other adults wishes are secondary.
The child's education will be the vital factor here , at 14 he is very near to taking exams and a change of school would almost certainly harm his chances. Continuing his education uninterrupted would be almost certainly what a court would order unless there was a VERY urgent reason to move him.