@Doomroar
I don't recall Grisha ever being manipulative towards Eren. Are you referring to the visions of his dad memories by 'brainwashing'? If so, i really don't think so, Eren begun taking drastic measures because the situation for Paradis island is in itself drastic and desperate, the whole world already wanted to exterminate them regardless of his actions at Marley. The Eldian cause has nothing to do with this.
I don't know what you mean 'by the royal blood', Eren is not royal, he wants to use the founding titan powers to secure the safety and freedom for his homeland and his friends, regardless if they're Eldian or not.
Also, it was obvious all along he wasn't planning to go along with Zeke's plan, but he needed him for his royal blood to activate the founding titan and command the titans inside the walls, it was all an act. Just as it's obvious all the things he said to Armin and Mikasa are bs.
All of Eren actions since the beginning have always spurred from his outrage at the enemies that would limit the freedom and safety of himself and the people he cares about.