in oblivion the night mother is a dunmer ghost and her and her five children skeletons are buried in the same tomb and in skyrim the night mother is a

draugr like corpse with actual eyes and hair is she coming back to life to lead the dark brotherhood again or what exactly is happening to her?

In many cultures body and spirit are two different things. A corpse may be in a coffin in a graveyard but its spirit may roam restlessly through a house. So I don't see anything odd about her being a spirit in Oblivion and a corpse in Skyrim.

That said, the Night Mother has changed slightly from game to game. In Morrowind she was rumored to be a living Imperial woman.