As these walls appear to be load bering, I'd probably call a proper mason if your really looking to repair the cracks.
On the cheap and easy side, you could probably use this:
If you really, want to try to repair the crack yourself, I found this:
How to do brick / concrete repairs
I edited the content, here is the jist:
Begin by cleaning all crumbling brick and mortar from the crack with a
cold chisel and sledgehammer. Where the crack runs through a brick or
a concrete block, use a brick chisel, angled into the crack, to widen
and undercut the break.
Enlarge the crack to a consistent width and clean the inside of the
crack to its full depth, or as far in as you can reach. Wire-brush the
crack, inside and out, to remove debris, then flush it thoroughly with
water from a garden hose. Cracks that affect only a single layer of
brick can be filled with mortar. Mix a small amount of mortar
according to the directions on the package. Spread a little mortar on
a scrap of corrugated cardboard, where it will dry quickly and reveal
its true color.
Mix enough mortar to fill the crack. Spray the crack thoroughly with
the garden hose. Fill the crack with mortar using a small, sharp
trowel to force the mortar into the full depth of the crack. Treat the
crack as one long joint, filling cleaned-out joints and the gaps in
broken bricks or concrete block evenly all along the crack.
When the crack is solidly packed with mortar, finish the surface with
a jointer and the trowel. Match the old joints where the crack follows
a joint: trowel the mortar to match the surface where the mended
surface is block or brick.
Let the crack cure thoroughly for at least 1 week. Spray the patched
area lightly with the garden hose several times a day during the