If we assume that Zeke's flashbacks were in chronological order, then him and Yelena were planning to overthrow Marley before Zeke learnt of Eren's existence and that he possessed the FT (also he hadn't found any suitable candidate until he directly asked Eren). This in line with the way ZE didn't touch in Marley and went all the way to cripple them, however how does that fit in with going to war with the rest of world?

Furthermore, Yelena is fully aware of Zeke's plan which I suspected would be the case because she thinks the sun shines out of his arse (and after this chapter it actually did so she's not even wrong anymore lol), but she also specifically mentions not to want the eldian empire reformed because they used to be just like Marley now. So her action are in line, but that does mean that the plan to fight back with the rumbling and against Marley was part of Zeke's plan for real (euthanasia getting rid of Marley)?

And last, Zeke asks Eren very politely if he wants to join him, what would he have done if Eren said "nii-san you're talking shit" and refuse to? He didn't have any other trusted candidate at that point?