In Sefer HaYashar, Perek 25, it lists the grandsons of Avraham and Keturah. However, in Tanakh (Chayei Sarah and Divrei HaYamim), it specifically choses to only tell us the names of Yokshan and Midian's children. Why does the Torah only choose the children of Yokshan and Midian if any of Keturah's grandchildren? To clarify, I am looking for reasons as to why Yokshan and Midian are so special that their sons are mentioned by the Torah as apposed to the others.
Radak to 25:3 says that the others may not have had sons, or that they died afterwards:
אפשר שלא היו להם או היו להם ומתו
I found an answer in מדרש תנחומא חיי שרה סימן ו:
R. Levi said: He is the one concerning whom the Holy One, blessed be He, said: All the nations of the earth shall be blessed through him (Gen. 18:18). During the generation of the separation, the sea inundated the world and the descendants of Ham were scattered (as thirty families), as it is said: The Lord scattered them abroad (Gen. 11:8). But now, the Holy One, blessed be He, said to him: I will cause them to descend from you, as it is said: All the nations of the earth will be blessed through him. He begot the (thirty) families, and these are they: the twelve princes that descended from Ishmael (ibid. 25:12—16), the sixteen offspring from his wife Keturah (ibid., vv. 1—4), and the two nations in the womb of Rebecca (ibid., v. 23). Hence Scripture says: All the nations of the earth will be blessed through him.
Therefore, the Torah mentioned those particular people who founded nations so that we can see that 30 nations came out of Avrohom.