Seems about right ... white haired dude is 100% sus .
Yet no one recognized him or accidentally blurted out his identity or, since almost everyone would obviously know about such a famous person, wondered why he wasn't present on the battlefield? I mean from what we've heard about him so far it seems only the ML has made him out to be so cowardly so it's unlikely that other people thought of him that way. Which means, in turn, it's hard to believe that anyone would think it's 'normal' for him to not be leading his division in the battlefield. So his absence should be noted. Yet it wasn't. So unless the ML calls him a coward the way he does because he's the only one who knew that the person leading the second division in battle was a subordinate in full body armor, I think it's far more likely that he grew up in Orsha, for some reason or another, with one of his parents who was (also) a noble and only discovered his true identity just prior to killing Estella.
Your point about Liam does make sense though. And perhaps that's why Louis didn't tell the ML the truth. Because he wanted him to kill, wound or imprison Liam.
I don't think the killer is related to her in any way, but I do have a feeling that she will become one of the targets of the killer..
and I think khalid and the white haired 2nd knight leader is the same person.. so that explains why that khalid betrayed and killed her in the past.. could be a secret mission that's why he is assuming another identity..
liam on the other hand is there to take revenge on the "khalid" that betrayed them..
this is just a theory...