Who says the brick are shifting?
The wood frame structure shrinks with time, resulting in a differential movement that can crack mortar joints.
Differential movement is common, but usually not seen in very many 2 story structures. For larger structure made from material more stable than wood (steel, concrete, masonry) there are requirements for the used of "soft" horizontal joints at about every other floor and your home is not far from that limit.
Brick veneer is connected to the structural back-up with flexible ties to allow the movement, but openings and corners are stress concentration points. Wood moves and shrinks more than other materials, so that makes problems more common.
Have the cracks ground out and tuck pointed with a similar colored mortar to minimize moisture intrusion and for cosmetic purposes.