Tribes consist of clans. The sheikh is the leader of the tribe. Under the sheikh, there are mukhtars who are each responsible for a number of families, sometimes even a hundred depending on the size of the clan of which they are a member. If a mukhtar cannot resolve an issue, then it is escalated to the sheikh.
There are 'baban' — meaning 'fathers' literally but here meaning 'forefathers' — who establish their own clans and tribes, but in everyday usage the Ezidis refer to every tribe, sub-tribe, clan, and so forth as عشيرة and refer to them in English equally loosely as tribes. However, academically speaking, there should be a level of 'tribe' (قبيلة) and then 'clan' (عشيرة) beneath it according to formal Arabic.