Coracobrachialis is the first muscle that gets innervation. it is involved in the flexing of shoulder and its adducts at the glenohumeral point. It does not cross elbow joint that's why it has no function there.
Brachialis is the essential versatile flexor of elbow joint. It originates at the upper arm almost mid of humerus, from the distal portion and inserts on ulna. that is why it can not have any kind of influence on shoulder.