activating stone Guardians?

I've done two runs with 3 hero's 2 henchmen and both times the non boss guardians never popped just the boss, is there a trick? Or do they some times not spawn or what?

Kill around 50 enemys or kill the warrior boss the is on the right side. Mahr Stonebreaker.

You have to go near the Warrior boss to start all the Guardians.
Aggro and kill the Warrior boss, then go to the pillars near him, and the pops should come out. Personally I went left from Altrum and killed the three other bosses, the continued south and grabbed the Warrior boss last, popped his stone guardians (2 sets) and back tracked the way I came, the guardians were all waiting for me, and without their bosses nearby.

Thanks, first run I had gotten lost and ended up going down the wrong passage before finding the carvings so must have killed enough by then.

It's quicker to start to the right first, going and killing the warrior boss and two groups of Stone enemies near him, and then retracing your steps to go to the left side and the three bosses. If doing it in HM, you might want to pull the three bosses before aggroing their respective spawns of stone enemies.

Have fun