The man on Wilhelm's left is Franz Joseph, the emperor of Austria and king of Hungary. {edit} I will retract this identification, since Franz Joseph was much shorter than Kaiser Wilhelm. The man in this photo is to tall to be the ruler of Austria Hungary.

The guy on the left of Wilhelm is Luitpold, Prince Regent of Bavaria (r.1886-1912).

As /u/davratta has correctly pointed out, the gentleman to Wilhelm's left is Franz Josef.

To Wilhelm's right is, I'm pretty sure, Luitpold, Prince Regent of Bavaria, who was acting in place of his nephew, Otto, who had been declared insane.