Unable to select model's bone

I have 2 models in my scene. They are stacked over each other because I want them to be in the same pose.

I want to rotate one model’s arm bone.
However, I seem to be unable to do so.
It always selects the other model’s arm bone instead.

To tell blender which bone I want to rotate, I select "PCL3" in the outliner.
This makes the model red (or its bones if I select "Armature" instead).

However, I still can not click this model’s bones to rotate them.

I only allows me to change "Genesis2Female" model’s bone instead.

Why?

Thank you!

In this screenshot you can see the model is red. I want to edit this model’s bones, but blender doesn’t let me.