Hi Emma,
The constant eye contact between the both of you would suggest that there is some mutual attraction.
However, that attraction isn’t strong enough for him to feel compelled to make a move on you or initiate conversation.
He isn’t all that intrigued by you.
The length of time it would take him to respond to your messages on messenger also indicates this.
Sometimes he would take hours or even a day.
He has most likely come to a point where he feels that, though he may find you to be attractive, he isn’t intrigued enough by you to want to take the risk on pursuing you in a romantic capacity.
He isn’t necessarily shy nor uninterested.
He seems like a relatively social guy.
After all, he does have friends and he also didn’t hesitate to make a joke out of the situation where you were unable to get that empty seat on the bus due to the friend of a passenger taking it.
If you are too shy to start talking to him in person because he is always with his friends or brother, try to find out about what other extracurricular activities he is involved in at school.
There is a chance that he could be a part of some school club, organization or event.
If he is, this would be your opportunity to join that group.
It will give you the best chance at getting to interact with him more and even getting him to talk to you on more of a one on one basis without his friends or brother getting in the way.