Is there a reason why the king of Belgium and the king of Bulgaria wore their sashes from their right shoulder to their left hip when the other kings in this picture wear it from left shoulder to right hip?
Was this a religious thing of something cultural?
It depends on the order the sash is representing.
The Belgian king Albert I is wearing The Order of Leopold which is to be worn over the right shoulder
Wilhelm I and King George V I guess are wearing Order of the Garter sashes which are worn from the left shoulder.
Edit: did a bit more research. It seems that seven kings wore the Order of the Garter. Albert I of Belgium wears the Order of Leopold as he only received the Order of the Garter in 1914. I'm guessing Tsar Ferdinand is wearing the Bulgarian order of the Saints Cyril and Methodius but that's entirely based on the more unusual cross in the middle of his chest.