Been awhile since I read the original ones, so can't help you with the Descolata, sorry.
As for chronolgy, Ender's Game and Ender's Shadow happen at the same time, from different viewpoints. Ender goes on to have adventures in outer space, which means he is traveling at light speed and so is living hundreds of years later, earth time. So his books are Speaker for the Dead, Xenocide, and Children of the Mind. The shadow books continue on from Ender's Game/Shadow directly, Shadow of the Hegemon and Shadow Puppets. I would read them as follows:
Ender's Game
Ender's Shadow
Shadow of the Hegemon
Shadow Puppets
re-read Ender's Game (optional)
Speaker for the Dead
Xenocide
Children of the Mind