There's something I don't understand, no matter how much I turn it over in my head: if Fritz was the royal family and had the Founding Titan; why was it the Reiss family that had the Coordinate and was the true royal family inside the Walls ? Have I missed something ?
The Founding Titan gave the Coordinate power to the Reiss family because he could control them. He could ensure that his purpose continued on. According to Rod, a Reiss who become the Coordinate inherits “the philosophy of the First King” (ch64). No Reiss had ever broken free of it. Rod speaks of it as a good and noble thing, but in ch67, Historia and Levi aren’t so flattering. Levi calls it brainwashing, while Historia says, “they are controlled by an ideology that won’t let mankind be free of the titans.
Pre-wall, the Reiss family were probably nobles. There are many noble bloodlines within the walls. These family lines are most likely the descendants of the original nine titans. The Fritz family is royal line. They are direct descendants of the Founding Titan, Ymir Fritz.
Having the coordinate, being given that power, made the Reiss family the true royal family within the walls. But they are not the true royal family.