Each WHM gets an individual buff listing the number of confessions they've applied. In a double WHM comp this means it's possible to see two confession buffs which can lead to confusion.
I find the easiest way to mitigate this confusion is to not look at the confession stacks and instead just keep an eye on your Plenary Indulgence cooldown instead. Since you're guaranteed application it's pretty easy to count how many stacks you'll have after you AoE heal a few times. That way you can just ignore the buff icon itself and just focus on using it when you see the skill itself is off CD. If someone doesn't get an application because they're too far away then chances are they'll also be out of range of your PI as well and it's kinda their loss if the WHM is positioned properly for maximum effective range.