The Witches of Dathomir were a group of clans who resided on the dark world of Dathomir in the outer rim, and tapped into a mystical power known as Shadow Magicks, which in reality was just the force. The witches of Dathomir Rancor and Witches of Dathomir riding rancor is a story that goes back millenia, to the Dawn of the Jedi. Nightsisters are a single clan on Dathomir!
After learning of these dark magicks on their planet, the witches soon split into many clans with the Nightsisters rising to be the most prominent and powerful, becoming the leaders of Dathomir… But what really separated the witches of Dathomir from the Sith and other dark side using cults was that they never fell to the darkness and never became slaves to it. They utilized it in their daily life and embraced its power where needed, without taking things too far… Something which the Sith could never achieve.
Soon after being taught of the magical ichor or dark force that flowed through their planet by an Exiled Jedi named Master Allya, the witches split into several clans. These were the Nightsister Clan, led by Mother Talzin, the Singing Mountain Clan, The Blue Coral Divers Clan, and the Howling Crag Clan. Being an exiled Jedi, Master Allya taught these clans of the dark side of the force and instilled a deep hatred of the Jedi within them, which carried down for generations.
She also taught the Nightsister clans how to tow the line between using the dark side as a tool, without allowing it to consume them. As a result, the Dathomirian were capable of loving others and showing genuine affection for others without any personal gain or thoughts of betrayal. Although the Jedi texts deep inside the temple vault deny this, it is believed that because the Witches are born and grow up on Dathomir which is a natural conduit for the dark side, they have a higher tolerance for it and can channel dark magicks without being corrupted.