So I jam with two guys with acoustic guitars. They mainly strum chord progressions and I normally by the same corresponding chords. However on some songs they 'Capo' their guitars.

So my question is, how can I easily and quickly play in the same key without using a Capo?
So you guys just play the same chord progressions with the same voicings? Im not sure if I can encourage that kind of behavior. Also with three guitars?
barre chord mean u put ur index finger over the strings like a capo would