How did owl know about Mikasa and Armin?

This ability allows those who hold the power of the Attack Titan to make their move and fight for their freedom. So, the reason why Kruger was aware of Mikasa and Armin before they were even born is that he saw the memories of the future inheritor of the power of the Attack Titan.

Is Grisha Yeager the owl?

As Gross is devoured, Kruger asked Grisha if he enjoyed such a sight. He then revealed that he was The Owl and claimed that he would show Grisha how to truly use the power of the Titans. Kruger then transformed into a Titan and destroyed the steamboat that took all the soldiers to the island.

How did Eren Kruger get the Attack Titan?

Grisha was confused by these names, and Kruger admitted that he did not know whose memories he was seeing. Afterwards, Kruger willingly allows himself to be eaten by Grisha, successfully transferring the Attack Titan to him.

Are Eren Yeager and Eren Kruger the same person?

Eren Kruger aka ‘The Owl’ is not the same person as Eren Jeager.