Darth Abonis
Nightsister magick had always been thought to be a different expression of the Force, like a different radio frequency but in light of TCW's The Disappeared arc and the destruction of the EU, I believe that Nightsister magic is something entirely different and not determined from genetic predisposition.
Proof: Talzin says she is not a natural force user and seeks to steal the living force from others so she can enhance her powers to be stronger than the Jedi or Sith combined. She has no power over the Living Force and needs to forcibly acquire it. Through magic she is able to emulate powers that Force sensitive's have. e.g. Force Lightning and Telekinesis. She is able to even enhance the inherent Force abilities in others e.g. (Savage Oppress) by possibly multiplying the existing midi-chlorians in his body or even supercharging the existing ones, giving him a Force potential, far greater than his norm. Talzin gave Maul to Sidious, probably because he was Force-sensitive naturally, more so than Savage. The Nightsisters that fought the droids during the Battle of Dathomir exhibited no Force-enhanced battle aptitude, and the 2 that fought Count Dooku may have been Force-sensitive as they were regarded as the Coven's greatest warriors.
Conclusion: Anybody can learn Nightsister magic, though it helps to be Force-sensitive as well.
Proof: Talzin says she is not a natural force user and seeks to steal the living force from others so she can enhance her powers to be stronger than the Jedi or Sith combined. She has no power over the Living Force and needs to forcibly acquire it. Through magic she is able to emulate powers that Force sensitive's have. e.g. Force Lightning and Telekinesis. She is able to even enhance the inherent Force abilities in others e.g. (Savage Oppress) by possibly multiplying the existing midi-chlorians in his body or even supercharging the existing ones, giving him a Force potential, far greater than his norm. Talzin gave Maul to Sidious, probably because he was Force-sensitive naturally, more so than Savage. The Nightsisters that fought the droids during the Battle of Dathomir exhibited no Force-enhanced battle aptitude, and the 2 that fought Count Dooku may have been Force-sensitive as they were regarded as the Coven's greatest warriors.
Conclusion: Anybody can learn Nightsister magic, though it helps to be Force-sensitive as well.