Why the use of twin tails? On a number of aircraft such as the:

Antonov 225:

   

A10:



F35:



Use twin tail designs. I understand for military aircraft that the benefit is it allows for a small tail cross section. Reducing the chance of it being damaged in combat. 

In the case of the A225 and other similarly designed cargo aircraft it means the rear of the aircraft can be more easily designed as a cargo hatch.

Are there any other reasons why a twin tail design is preferable over a single tail design?
This constructive solution can be dictated by a number of reasons: 

Aerodynamics - for AN 225, 747 Shuttle Carrier Aircraft, A-10 (control surfaces are more effective outside turbulent air); 

Some sort of redundancy - for military airplanes F-35, A-10;

Easier construction - since the surface being smaller aerodynamic loads are smaller the structure can be lighter wight;

Radar cross section - F-35, SR-71;

Stability considerations: the arm for the vertical surfaces is a little longer than the arm of a potentially single surface on the longitudinal axis of the aircraft, so the two vertical surfaces combined can have a less surface area than a potentially single surface.