Seat post clamp bolts are easily replaced with quick-releases.
The 9/16 could be taken down to 14 mm easily with a modest amount of grinding skill. The 1/2 and the 13 mm are close enough to work with the same 13 mm wrench. Or the same application of grinding skill can turn the 13 mm to a 1/2".
A little more application of a little more grinding skill will turn 13, 14, 9/16 and 16 mm into 1/2".
Or buy wrenches, cut them in half and ask someone to weld the desired halves together. Maybe first take the 13 mm nuts to 1/2", and the 9/16 to 14 mm. Then make custom wrench that's 1/2 at one end 14 mm at the other.