Can we, a group of nine, go from Xian to Dunhuang via Lanzhou by bullet train?

There is no bullet train for this journey. There is one direct train K591 running between them. It takes about 22 hours 40 minutes. If you go to Lanzhou first, it takes about 7~8 hours. Then it takes about 13~14 hours by train from Lanzhou to Dunhuang. It totally takes about 20~22 hours excluding the waiting time.