So do I. The spec says it's a 14 mm open end wrench. I measured mine - it's 14 mm all right. Perhaps you can use the other end to grab the brake body by the springs, if you cannot fit the 14mm open end wrench around the flats.

The original model OBW-1 had two offset open ended wrenches: 10mm and 13mm. If the 14mm open wrench does not fit your 12mm flats, it's unlikely the 13mm would.

I use a drop bolt for my sidepull brakes. The dropout completely replaces the brake's mounting bolt, including the flat. The dropbolt has flats that are used for centering.

If you are using the dropbolts that you showed, then there should be no reason why you should not be able to center the brakes using the dropbolt's flats. There also appears to be a set screw in the picture you provided that appears to lock the brake mounting screw in place. Perhaps, if you opened the set screw a bit, you would be able to rotate the brake by hand without upsetting the dropbolt's orientation.

Of course, you could always use the brake's centering set screw for centering the brake, if the adjustment is minor.

Perhaps, a photo would be in order, for us to diagnose what appears to be a non-standard problem.