For Balthier, family is very mildly discussed, and has remained a mystery for a large portion of the game. Because of the conditions, not very much is known about his family outside the game itself.

Balthier's father, Doctor cidolfus Demen Bunansa, as presented by the game. Balthier first brings up the fact that he's his father upon the party's arrival at Phon Coast. One of the only people to address him by his real name nowadays, Cid is anything but the ideal father. Emotionally torn from watching his father being eat away by his own ambition, Balthier left his former life behind him. Because I am unwilling to retell the story (read: lazy!) of Balthier's history with his father, you may find the details and such of it here.

In Final Fantasy XII: Ultimania Omega, it has stated in the timeline that Balthier was the third son of Doctor Cidolfus Bunansa, meaning he has two other brothers whose birth preceeded his. The game fails to make any mention of any older brothers Balthier has, and their significance in Balthier's past seems unimportant and almost non-existant. However, this does clear up a few mysteries: for one, he is not an only child. Secondly, Balthier would be the sole "prodigial" son of his siblings; the timeline states that Cid gave up on his son and turned to Vayne instead, not to any of his other children. Of course, any sisters or younger brothers that Balthier might have isn't noted anywhere. Nevertheless, siblings of a few characters were not brought up throughout the game either, such as Penelo's brother who died during the war, or Ashe's eight (possibly more) other siblings!

Final Fantasy Tactics presents a playable minor character by the name of Mustadio Bunanza. Although there is no confirmed connection to Balthier himself, the similarities are almost uncanny. Both characters weild a gun and seem to share an interest in the mechanics of airships; the only difference in their interests are that guns and airships are of ancient relics in FFT. Pehaps the most notable similarity is their last name. Although Mustadio's surname is spelled "Bunanza", Balthier's "Bunansa" spelling is a transliteration error (most likely intended, if anything). In Japanese, Mustadio's name is spelled ムスタデオ・ブナンザ. Likewise, Balthier's real name (Famran Mid Bunansa) is written in Katakana as ファムラン・ミド・ブナンザ; his last name would be directly translated as "Bunanza". Moreoever, their last names are far from a coincidence. As stated in the timeline, Tactics takes place several years after the events of Final Fantasy XII. Since both games share the same world, it's safe to say that any blood relation from Mustadio to Balthier is anything but impossible.