direct them to this site?
explain the concept that they are putting strain on their body, and that the body needs time to recover and supercompensate before the next bout to be effective.
get talking to some big guys in the gym and find the ones that train 2-3-4 times a week and get the to talk to your mates.
personal trainer.
ask them if they really want to get bigger. if the answer is yes, then are they prepared to find out how to get bigger. if answer is yes, tell them to go do said research so they can learn for themselves.
i did 3 sessions with a footy player trying to bulk up, made him stay out of the gym, only come in 3 times per week. the guy exploded, 4kg in 3wks.