Probably the 3 in the classroom that have bombs strapped to them. You can't let them get touched by the fire zombies. --- PSN ID: RyuuHou24 "I never said that....and even if I said it, I never said it" - Dr Peter Venkman RGB
If it is the 3 guys with bombs strapped (the part with the pole dancing), the best method that I used is kill the 3 fire zombies first. After that then use the pole. That I noticed if you use the pole first, the fire zombies usually are still locked onto the surviors and killing them. The other zombies won't even appear till you jump on the pole so they will mostly all die anyways from it too.
Make sure you walk near them to get the medals they're carrying after you save them. The game doesn't register them as being saved if you just walk away after killing all the zombies that are coming after them.