The Sapa Inca owned everything. He ruled everything. He made all the laws. He was all powerful. Many Sapa Incas came to power over time. Each was the head of government.
Each Sapa Inca put his relatives, along with the nobles, in positions of power, to help him rule the Inca empire. Each Sapa Inca had four top advisors, who make sure the relatives and nobles did the work they were assigned to do.
When a new law was put in place by the Sapa Inca, word went down the line from the top officials until it reached the bottom officials, and from there to the common people. Since the common people had no say in government, that was the law until a new law came down.
This system worked well, and the Inca population grew to about 12 million people.