Where and how was Diavolo hiding where he was after the body swaps of Silver Chariot Requiem?
Diavolo's Soul, which is attached to King Crimson, was "set free" by Silver Chariot Requiem.

Much like he shared a body with Doppio (without having full control), the same thing happened with Mista's body, now being inhabitted by the soul of Trish. Assuming Diavolo had no choice who he swapped with, this fact stands as mere coincidence.

Doppio had no idea he was being inhabited by the boss, therefore it stands to reason the same thing is true with Trish and her soul in Mista's body.

Using Mista's body &amp; King Crimson, Diavolo managed to kill Narancia in Giorno's body undetected.

If you watch the scene, Mista seems to be the closest to where Giorno's body (inhabited by Narancia) was strung up.