Two ways around this:
1) Load into the practice room, as many cabinets and amps you can get your hands on, PA subs and power amps,
take up the whole back wall to the roof, and play your loudest.
Then show them that if you are to keep up wit the guitars, then this is the way it has to be.
2) You, the drummer, the singer play super quietly, keep turning down, until the guitarists get the picture,
even make a recording of your practice session, mic'ing the room and recording in front of the guitar cabs, so the recording is 98% guitars.
Then play it back to the band, and ask them if this is the right sort of mix and balance the band should sound like.
one other option:
have the guitarists get their ears surgically moved to the backs of their knees so they can hear themselves.
1) Load into the practice room, as many cabinets and amps you can get your hands on, PA subs and power amps,
take up the whole back wall to the roof, and play your loudest.
Then show them that if you are to keep up wit the guitars, then this is the way it has to be.
2) You, the drummer, the singer play super quietly, keep turning down, until the guitarists get the picture,
even make a recording of your practice session, mic'ing the room and recording in front of the guitar cabs, so the recording is 98% guitars.
Then play it back to the band, and ask them if this is the right sort of mix and balance the band should sound like.
one other option:
have the guitarists get their ears surgically moved to the backs of their knees so they can hear themselves.