Ill explain the planets in detail when we get to each particular one, right now ill type in what the Hierarchy looks like:

1. Earth - The Heart of the Empire

2. Atheros

3. Terran

4. Helios

5. Umbros

6. Sothis

7. Zerith

Structure of Nobility

Basically:

The emperor rules over all 7 planets

Each planet is ruled by a Duke

Each planet has 2 marquises under the Duke whom are responsible for half of each planet

Each country is ruled by a count

Each Viscount rules a province

Each Baron rules a city/town

Also Earth has an archduke, and 3 marquises 

This stuff is pretty basic as of now but ill introduce information step by step as we progress.