According to the Basic Rules:
Initiative determines the order of turns during combat. When combat starts, every participant makes a Dexterity check to determine their place in the initiative order. The DM makes one roll for an entire group of identical creatures, so each member of the group acts at the same time.
Does that mean that the creatures of the same type share a turn, or only have the same initiative? If they go on the same turn, it gives a significant advantage to enemies with pack tactics, and makes "wakeup chains" against sleep/hypnotic pattern stronger.