I'm plan to go GHZ to Xiamen on 12 nov by train:-

They departs from different stations, Z297 departs from Guangzhou East, Z299 departs from Guangzhou station instead. Usually they begin for sale 60 days in advance. If you want 4 people for the whole cabin, you would need soft sleeper cabin. But as i can see from the ticket availability, the soft sleeper are very hard to get for this trip. With limited availability, it may very hard to make sure if you can get a whole cabin of your own.