They shoould have made Zhang Bao and Zhang Liang playable, because the only playable character for the Yellow Turbans is Zhang Jiao, so you don't have a choice. They could have given those two different elemental powers. Since Zhang Jiao's element is fire, Zhang Bao's could be ice and Zhang Liang's could be lightning, I guess.
They shoould have made Zhang Bao and Zhang Liang playable, because the only playable character for the Yellow Turbans is Zhang Jiao, so you don't have a choice. They could have given those two different elemental powers. Since Zhang Jiao's element is fire, Zhang Bao's could be ice and Zhang Liang's could be lightning, I guess.