...in translation ES > EN.

Let's see: The origins of the phrase, as I have been told (and this might be apochryphal or at least inaccurate, but it works well enough in this case) are that a King of Aragón in the upper Middle Ageshad been informed about a possible revolt by a number of notables, whereupon he decided to order them all to his castle and then have his guard dispose of them.

Just when, with the suspects there, he was about to give the order to kill them all, the chief of the guard detail whispered on his ear:

"Ni son todos los que están, ni están todos los que son"

That is: Not all the rebels were present, not all present were rebels

The point is, while adding "rebels" makes it perfectly clear, by using the "ser" and "estar" here, without determinants, you get a "jack-of-all-trades" phrase in Spanish, which I have been unable to translate into English AS SUCH, that is, as a jack-of-all-trades phrase, because I CANNOT find an equally ambiguously translation -since you use "to be" in both cases, you MUST qualify the verb (or I cannot find how not to).

And this is the point: I believe that this is the case here, and I am still at a loss...