no you cant die from peyote, that is unless you take a shit load of it and overdose on mescaline (which is extremely rare). they'll proberbly want to puke because it will taste nasty but if they dont they wont die.
mescaline is the chemical thats in peyote that makes you trip, its also in some other legal cacti such as san pedro and pervurian torch. mescaline is a really safe drug, i recently made a tea out of san pedro, i estimated i consumed around 400mg of mescaline based on the weight and size of the cactus. just make sure your friends now about dosages for peyote, have'em check out erowid.org