who is the first mentioned son?
He was the Grand Duke of Lithuania.
Jaunutis
aunutis (, ; literally "young man"; baptized: Ioann, "Jawnuta", "John" or "Ivan"; ca. 1300 – after 1366) was the Grand Duke of Lithuania from his father Gediminas' death in 1341 until he was deposed by his elder brothers Algirdas and Kęstutis in 1345.

what is family of gediminas? A group of family members of Gediminas, Grand Duke of Lithuania. what are its origins? Various theories have claimed that Gediminas was either his predecessor Grand Duke Vytenis' son, his brother, his cousin, or his hostler. what is the origin of this former mentioned predecessor? UNANSWERABLE what are its wives? The Bychowiec Chronicle mentions three wives: Vida, Olga , and Jewna. who is the last mentioned wife? She was the daughter of Prince Ivan. who are the sons? Eight sons: Jaunutis, Kęstutis,  Algirdas and others.
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Jaunutis [SEP] Introduction
Others claimed that Jaunutis was the eldest son of Gediminas' second wife; thus the tradition that Gediminas was married twice: to a pagan and to an Orthodox duchess. Another claim is that he was living with Gediminas at the time of his death, and so he was naturally a successor to rule Vilnius and Lithuania.