Train Travel in September from Zhangjiajie to Chongqing via Huaihua

I am hoping to travel by train from Zhangjiajie to Chongqing via Huaihua and also from Chongqing to Chengdu in September. Will I be able to buy tickets a few days in advance from the stations by presenting my passport or will my hotel be able to purchase them for me. I'm hoping to get an overnight sleeper for the Huaihua to Chongqing leg. I don't speak much Chinese