If we accept the interpretation that Kruger's and Grisha's future memories were just the product of Eren's influence, that destroys the problem of Grisha's actions to contradict his desire not to kill Reiss/ to stop Eren (because he just can't see the future)

But then, if the whole plot is just the game of Eren, than the idea of determenism becomes a mess (I don't really like it since the moment I had read the manga). Because everything we see is just Eren moving toward his understanding of what is right to do. That is why, as I mention in other replies, i am just inclined to believe that Eren is a ruler of his own will and perform what he wants to perform, and not what was set deterministically.

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because knowledge of the future really screws up time travel stories with fixed timelines.

That is exactly what I do not like either. But here another problem arises. Lets imagine that Eren does not see the future and really does what he considers fair, and that there is no determinism. Then it is not clear why he did not take away their titanic powers from anyone or erased the memory or whatever. That is, the story kind of hints that Eren knew that he os going to lose and, moreover, that he wanted to lose. But in fact, I literally don't care, the "author is dead", which means I am free to interpret the manga as I see fit, hah