Garden wall cracked - best way to fix

Froggitt2

So bit more information, if the wall is two bricks deep, which it seems that it is, the posts are not attached to my layer of bricks, just the neighbours. Not the fence sails are not causing the problem to the wall.....my half of the wall at least. But I'd still like to reinforce the wall anyway.

Froggitt2

btw this all came about because Storms Eunice Freddie and Gladys destroyed four fence panels and one post. So we've started clearing that mess up and ordering new panels/post, and I started clearing the bushes away from the wall, so we can get there to install the new panels. Clearing the bushes revealed the cracks in the wall.

stuart45

The smaller wall looks like a 9 inch wall and the taller one 4inch. If it's a retainer that's probably why it's cracked at that point. 
Weepholes like that aren't much use without a proper drainage system behind the wall. Hydrostatic force often wrecks a wall.