Why do Schottky diodes have two anodes?
It's a dual diode. There are two diodes in one package. 



You can parallel them if you want (connect 1 and 2) but there is no matching characteristics given, so you can't really depend on the rating to be much better, and the leakage will definitely double. 

The characteristics are for each device, however they are (obviously) tightly thermally coupled so the total power dissipation will have to be taken into account.