How do I copy bones from one armature to another? I have 2 armatures. I want to copy one subset of bones from the first armature to the second -- in Edit Mode -- in order to have the same bones, same names, same transforms on the second armature.

What I have tried:

A) in Edit Mode, Ctrl+C the bones from the first armature, CTRL+V to the second armature also in Edit Mode. This doesn't work because Copy/Paste will actually copy the entire Armature Object in Object Mode, and will paste a new object with all the bones.

B) in Edit Mode, Shift+D to duplicate the bones in the first armature, then try to unparent them from the first armature and parent them to the second. But I couldn't figure how to unparent the bones from the armature, all the unparenting options I could find would only unparent the bones from their current parent bone, but they'd stay inside the first armature.

Is there any way to do this in Blender or am I going to have to manually rebuild all the bones, one by one, on the second armature?
You were correct with your unparenting strategy. The shortcut to seperate a Bone is P. Then select your separate armature and Shift select the armature where you want the object to be and press Ctrl+J