In general, that's a bad situation because you have two versus one. Of course, this is no different than an Antagonist trying to fight two players at once. You are still giving a directional input to distinguish between targets. This isn't anything that favors Antagonists because they suffer from the same problem of accidental targeting. If anything, it actually favors the AI. However, since the Antagonist in your scenario is typically going to be the larger threat it would be suggested to down them first. Keep in mind, they can and still will shoot you even when downed. Thus, your safest option would be to not CQC them at all and simple shoot them to death and then perhaps CQC the Elite. Perhaps, in the future we might get some sort of lock-on system that might help but that will likely present challenges of its own.