As far as the title, depends what direction you wanna take it:
Coven: noun
an assembly of witches, especially a group of thirteen.
Covenant:
1.
an agreement, usually formal, between two or more persons to do or not do something specified.
2.
Law. an incidental clause in such an agreement.
3.
Ecclesiastical . a solemn agreement between the members of a church to act together in harmony with the precepts of the gospel.
4.
( initial capital letter ) History/Historical .
a.
National Covenant.
b.
Solemn League and Covenant.
5.
Bible.
a.
the conditional promises made to humanity by God, as revealed in Scripture.
b.
the agreement between God and the ancient Israelites, in which God promised to protect them if they kept His law and were faithful to Him.
I would suggest The Coven.
![Smile :)](./images/smilies/icon_e_smile.gif)
Perhaps a joker could be the 13th witch, or a sacrifice, or a diptych with them around a fire performing a ritual.