To study the relationship between the Seven Sages and their descendants, it is essential to study the background of each sage. Here I summarize the history of each sage and list who their possible descendants might be. The reasoning behind each choice is explained in the next section. If you already know about the sages, you can skip to the next section.

Princess Zelda - This young Hylian princess was destined to be the leader of all the Sages. After unintentionally allowing Ganondorf to enter the Sacred Realm, the Triforce of Wisdom was hidden in her heart, and she disguised herself as a Sheikah. Seven years later, when Link had awakened the five other imprisoned Sages, she helped Link in his battle with Ganon and told the Sages when to imprison the Evil King.
Her Descendant: Princess Zelda

Rauru - The ancient Sage of Light lived long before the other Sages, and helped to build the Temples of Light and Time to guard the Triforce from evil hands. Centuries later, his spirit was the only one left in the Chamber of the Sages until the other five were awakened.
Possible Descendants: Sahasrahla, The Loyal Sage

Saria - One of the ageless Kokiri, Saria was Link's life-long friend. Sensing evil spirits in the Forest Temple, she went there to see what was happening. She was imprisoned by evil monsters, and in her absence Kokiri Forest was overrun by monsters. Link, now the Hero of Time, defeated Phantom Ganon to awaken her as the Sage of Forest.
Possible Descendant: Sage in Kakariko Village

Darunia - While he was away from Goron City, Ganondorf's forces imprisoned almost the entire Goron populous inside of Death Mountain, intending to feed them to the awakened fire dragon Volvagia. Darunia went in after them even though he lacked the mystical Hammer. Link freed the Gorons and defeated Volvagia, awakening Darunia as the Sage of Fire.
Possible Descendant: Sage on Death Mountain

Ruto - After an evil spirit in the Water Temple froze over Zora's Domain, Princess Zelda, disguised as Sheik, managed to save the Zora Princess Ruto from under the ice. Since Ruto had secretly given Link the Zora's Sapphire in gratitude for saving her life, Link was technically engaged to be married to her. Seven years after this time, Link went to the Water Temple after Ruto and defeated Morpha, ending the curse on Zora's Domain and awakening Ruto as the Sage of Water.
Possible Descendant: ???

Impa - This Sheikah guardian of the royal family helped build Kakariko Village up from nothing. When evil spirits escaped from the well into the nearby Shadow Temple, she felt obligated to stop the evil undead creatures. Princess Zelda, disguised as Sheik, knew that her guardian Impa couldn't handle the task alone and urged Link to help her. Link defeated the evil shadow spirit Bongo Bongo and awakened her as the Sage of Shadow.
Possible Descendants: Impa, Sage in Kakariko Village, Sahasrahla

Nabooru - One of the desert-dwelling Gerudo thieves, Nabooru objected to her king Ganondorf's brutal method of thievery and schemed to mess up his plans. After sending young Link in to the Spirit Temple, Ganondorf's hideout, to obtain the Silver Gauntlets, she was imprisoned by the twin witch sisters Twinrova, brainwashed, and made a loyal servent of Ganondorf. Seven years later Link, the Hero of Time, saved her from the imprisonment of an Iron Knuckle suit, defeated the witches Koume and Kotake, and awakened her as the Sage of Spirit.
Possible Descendants: Aginah, Sahasrahla