Why is this "turisti"? According to https://en.wiktionary.org/wiki/turista#Declension, the plural nominative is "turisté" (and some other exercise in this lesson seems to agree).
Both turisti and turisté are correct. The first one is more colloquial, the second one more formal.
Bad train není špatný vlak?
wrong train - an incorrect train, going somewhere else or at some other time...
bad train - I don't know. Perhaps "Pendolino is a bad train, I prefer ... instead." but it is strange to board one.
Ti turisti nastoupili do špatného vlaku. spatneho vlaku is that because of do ?