Inquiry re bunk number (if there is) and nearest train station

We are 3 people traveling from Beijing to Shanghai. Can we be at the same cabin (we prefer to be in the 4 bunks cabin)? Is there an inidication in the ticket if you sleep in the lower bunk or upper bunk (like there's a bunk number) or is it a first come first serve basis?

Plus we plan to stay in Red Lantern House in Xicheng District in Beijing. Is it nearer Beijing South Train Station or Beijing Train Station?