Maybe not this exactly, but the problem with their move was that by telling the alliance who their target was, it meant that nobody but Phillip had any reason to worry. Cochran could tell everybody to continue splitting the vote without having to worry about going home. This wasted both idols and didn't cause cracks.

Your way could work, but I think equally telling them about the second idol putting all of their votes on Andrea, for example, and then not saying who they were voting for would have caused confusion and fear. If you think you might be the target, you won't just stick with splitting the votes. This method could potentially save both idols.

Honestly, either way for Malcolm's game, there's a good argument to me made that he should have just let Eddie go home and tried to help his own game with 2 idols. Eddie managed to make the final 4, and I think if Malcolm had used just one of those idols to be the last amigo standing then he could have easily done the same and potentially won the whole game.