Poet can be viewed as Morokei's older sister, due to her father/daughter relationship to Miraak. In kind, Morokei treats her as such, taking in her son as an apprentice.
Being head of the Order, Vahl is Morokei's master and the one who he answers to. Morokei is to Vahl as Vahl was to Miraak, meaning that Vahl is reminded of her deceased friend when with Morokei.
Miraak is Morokei's father, he passed on to Sovngarde when Morokei was only 10 years old.
Serana is Morokei's mother and she raised him single-handedly, for a good portion of his life.