The Assembly of Iron consists of Steelbreaker, Runemaster Molgeim, and Stormcaller Brundir. These three run the Iron Armies of Ulduar and Northrend.
In the Ulduar Constitution, Article I Section I gives Stormcaller Brundir only those "legislative powers herein granted" and proceeds to list those permissible actions in Article I Section 8, while Section 9 lists actions that are prohibited for him. The vesting clause in Article II places no limits on Steelbreaker, simply stating that, "Executive powers shall be vested to the biggest of the Iron Assembly of Ulduar." Runemaster Molgeim holds "The judicial Power" according to Article III, and it established the implication of Judicial review in Thorim vs Loken. The Ulduar Government refers to the three as "branches of government." Steelbreaker has attempted to usurp power from Stormcaller Brundir arguing for Separation of powers to include being the Commander in Chief of a standing army since the Civil war of the Giants, executive orders, emergency powers and security classifications since the war of the ancients, national security, signing statements, and now the concept of a unitary executive.
But enough of politics, the fight varies depending on the order that you kill the three. The standard method is Steelbreaker, then Molgeim, then Brundir. After you kill one the other two get more powers and when one is left he becomes even more powerful.