In Genesis 26:34 Basemath is the daughter of Elon the Hittite, and one of the three wives of Esau. In Genesis 36:2 she is called Adah, and is the only one of Esau's wives of whom his father Isaac approved, as the other two were both Canaanites.
In Genesis 36:3-4,10,13,17 Basemath is the daughter of Ishmael and another of the three wives of Esau. In Genesis 28:9 she is called Mahalath.
2 Esau took his wives of the daughters of Canaan; Adah the daughter of Elon the Hittite, and Aholibamah the daughter of Anah the daughter of Zibeon the Hivite; 3 And Bashemath, Ishmael's daughter, sister of Nebajoth.
4 And Adah bore to Esau, Eliphaz; and Bashemath bore Reuel; 5 And Aholibamah bore Jeush, and Jaalam, and Korah: These are the sons of Esau, who were born to him in the land of Canaan.
9 And these are the generations of Esau the father of the Edomites, in mount Seir: 10 These are the names of Esau's sons; Eliphaz the son of Adah the wife of Esau, Reuel the son of Bashemath the wife of Esau.