Here is the general principle to take away from Nate's answers:
Master of Whispers is NOT a claim replacement. Rather, it is more of a claim modifier - like an effect that raises or lowers the claim number on a player's plot. Effectively, any claim effect that resolves "by player" can be modified to apply to whichever players the attacking player wants (instead of the normal scheme of "only the defending player"). It can modify any claim effect (that takes place during the player's INT challenge) that is resolved "per player," but you have to pay careful attention to which ones are "per player" and which ones aren't. As such:
- Trial by Combat replaces the "per player" INT results with the "per player" MIL results, so it can be modified by Master of Whispers to reach more players.
- MMD replaces the "per player" results of the normal claim with the death of a single target character. So just like the death of the single target character cannot be modified to kill more characters if you have a claim of 2 or larger, it also cannot be modified to kill more characters controlled by more opponents if you have Master of Whispers.
- VfE, played by the defending player against Master of Whispers, will lock the chosen player in as the defending player for the challenge. Since VfE will be played after the attacking player has determined which players his modified INT claim will resolve against (this is part of determining the characteristics of the "when claim is applied" triggering condition), the defending player using VfE to deflect the claim that resolves for him/her to another player does not affect any player other than himself/herself and the player chosen to take his/her place. As such, VfE can be used to deflect the defending player's claim responsibility - as defending player - to another player (whether the Master of Whispers had them resolving claim or not), but cannot change any other choice of the attacking Master of Whispers for who else is on the hook for claim. NOTE: that a player chosen by both the Master of Whispers and the defending player triggering VfE would not resolve claim twice (because claim only resolves once). The double choice simply changes their resolution from happening as "other opposing player" (Master of Whispers) to "as if they were the defending player" (VfE).
(Note also that VfE can only be triggered by a losing, defending player; it cannot be triggered by any of the other players chosen to resolve claim.)
So, a good way to think of the interaction between claim replacement and Master of Whispers is that if the claim replacementeffect would sidestep claim number modifiers (e.g., MMD kills 1 character only, no matter what your claim is), it probably also sidesteps Master of Whispers. In the special case of VfE and Master of Whispers, the person using VfE can only move the claim responsibility away from them (and to one other person), not make, or re-make, all the claim choices for the Master of Whispers.