These 'Twelve Swords"... are they strong?"
"Well, their ranks are based on their power, and the Kaleesh female who nearly defeated me claimed to be number four.
—Mara Skywalker and Luke Skywalker
The Twelve Swords were a small group of highly skilled Imperial Knights under the direct command of Emperor Havelock Pahmus. The Twelve Swords consisted of twelve members at any given time, ranked in order of strength. A subdivision of Imperial Knights, these warriors were exceptionally attuned to the Force, having trained under the greatest instructors of the Order of the Imperial Knights and subjected to all kinds of training regiments deepening their connection to the Force. They were among the strongest Force-users in the known galaxy and more than capable of besting the strongest members of the Jedi Order in battle.
The Twelve Swords were masters of lightsaber combat, martial arts, strategic thinking and using the Force in battle, and were expected to be in peak physical and mental health at all times. In addition to their other strengths, expertise in a specific Force ability, often a self invented one, was something all of the Swords possessed, although whether this was a requirement or not was not known.
Each member of the Twelve Swords was chosen for their strong connection to the Force and superior combat ability and assigned a number from 1 to 12 that indicated their rank and relative power level, with number 1 being the strongest and number 12 the weakest. A member referred to himself/herself as "Sword" preceded by the number of their rank e.g. "The First Sword" in the case of Daash.
Though the number of a Sword clearly displayed his rank, the actual difference in power between the holders of the ranks could vary a great deal. The difference in power between two Swords might not be very big, but could then again be immense. For example, Hammin, the Eleventh Sword, was only slightly stronger than Fuuton Renkudamak, the Twelfth Sword, while by contrast Dago, the Sixth Sword, was considerably stronger than Endel Gyrannil, the Seventh Sword.