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In The Last Jedi we find out that
Luke started a training academy for future Jedi Knights. Ben Solo/Kylo Ren turned against Luke, burnt down the school and fled. He gathered a gang of followers around him from the ex-pupils and killed any who would not join him.
What happened to those pupils that sided with Kylo Ren? I think we see them gathered together in Rey's Force-vision in The Force Awakens.
Is there any further info on these characters in current canon?