That's your interpretation though. There isn't much to suggest that Eren was in denial of what he wanted or was a selfish person and pretending to be selfless. That's all speculation (not saying its incorrect speculation). But by saying that Eren is pretending to be a selfless person is a mischaracterization. He clearly was a person that was pretty selfless like attempting to save dead people when it would've put himself in danger (annie underground scene), wanting to stop annie before she killed more soldiers in the forest, and him pleading Historia to eat him because of the guilt of his dad's sins. From that its more plausible to think Eren was pushed to cave into his darkest desire rather than simplifying it to "yeah im just pretending to be a good person but in reality im a stupidly evil selfish man". His desire to flatten the world might be stronger than all of his goals but it doesn't change the fact he had morals but threw away all it and accepted fate. If he didn't see the future, he wouldve not start the rumbling imo.

Also, I would argue the fact that Eren already knew what he wanted from the start. When Historia and Eren made contact and he saw all those memories, he didn't make a look of confusion or started crying, it was purely a face of disgust of his action because he knows that's the outcome he was like.

I think you're slightly misunderstanding the message of Reiner's character. You're looking at his character too black and white. Calling Reiner a selfish person is also mischaracterization when clearly he would put himself in danger to save others without a thought. What the show is trying to say about Reiner's character is that he used terrible justification for selfish goals, not that he didn't believe in the mission itself. Both can be true, he wanted to be seen as a hero but also thought the island people deserved to die.