Contact - the information is carried on electrical currents, and so only the one holding the electrodes will be affected.
Remote - the information passes from the DNA in the nail directly to the target. It does not pass through normal space like a radio wave. Since the information is sent instantly and directly to the target, no one else can be affected. Even if they stand between you and the remote, nothing will happen as the information is not flowing through this space.
Plasma - Yes and no.
Yes in that the plasma has large area of effect. If I recall correctly, about 200 feet out, it can still be detected even with solid concrete walls in the way.
While the energy looses power the further you go from the source, there is enough energy to easily be efficacious past other rooms.
No in that if the frequency does not resonate with you, it will not affect you. However, if it does resonate with you, then yes it can have an effect.
A single frequency may affect other people and you at the same time, but for very different reasons.