This sentence is complex, and is easier to understand if we break it up.
Vader tries to persuade Luke to join him.
Vader tries to persuade Luke to embrace the Dark Side of the Force.
Vader tries to persuade Luke to overthrow the Emperor with him.
Both Luke and Vader are trying to overthrow the Emperor, but they have different goals in mind.
Luke is a Rebel who is trying to destroy the Empire and remove it from power.
Darth Vader is a high-ranking member of the Empire who wants to enact a coup, killing the Emperor and then taking control of the Empire for himself.
If Luke were to help Darth Vader overthrow the Emperor, he would be taking Vader's job while Vader becomes the new Emperor. They would crush the Rebellion and rule the galaxy together.