I am making a mod that involves Sauron (Dremora Race) and his orc minions (Falmer Race), but all of the Orcs (Falmer) always kill Sauron. I have tried messing with the relationship tab and setting Sauron as the parent of the orcs but they still kill him everytime. How can I make them allies?

It is to do with the Factions they are members of - Both need to be neutral, friend or Ally to the other

However, if these are Vanilla characters (NPCs) you would do much better to clone them, and then set the Faction Relationships of your clones ... Or you will break the characters in Vanilla (although that maybe what you want to do?)