1 is the "bad" ending if you don't disarm the bomb.If you disarm the bomb, you get the other 3.
Depending on who you bring with you to ascension peak, your characters and recruited, you will get different speeches from each (based on personality).
Blowing up the ship or not, aligning with the trang or umpani or both (or double-crossing them), have no bearing on the endings.
Tools for Wizardry(r) 7