Enumeration: "Xiong Er" = 10, brother is 0, "Xiong Da" has no value, because different Chinese characters represent different numbers;
"Xiong Er" = 12, "Xiong Da" can be 13, 14, 15, 16.
"Xiong Er" = 13, "Xiong Da" can be 14, 15 (omitted, numbers are repeated);
Xiong Er = 14, Xiong Da is worthless.
So the sum of the three digits represented by Brother Xiong is:12× (13+14+15)+13×14 = 686.
So the answer is: 686.