Book of Exodus
Reuel, also called Jethro, is Moses' father-in-law. When Moses saves his daughters from aggressive shepherds, he invites Moses over for dinner and gives him his daughter Zipporah as a wife (2:18).
But he's not just an over-the-top gift giver. He also comes up with the idea for the whole Judges system. Instead of having Moses listen to the Israelites' disputes every single day, he suggests splitting up the job. In this way, Jethro is one of the few outside influences we see plainly at work in the text. After all, anything Egyptian is abhorred, and while Mesopotamian literary themes are at work, they're invisible. But here, the Bible explicitly says that the Israelites got an idea for their political and legal system from a regional source. Nifty.
Moses's mom, Jochebed, doesn't get much screen time. She basically comes onto the scene, puts Moses into the Nile, and then gets to hang out with him while he's a baby. So why do we care? Because family—particularly origin stories—matters in the Bible. The fact that Moses comes from humble beginnings makes his ascent all the more powerful.
Modern adaptations of Exodus have to address some of the issues that the Bible skips—like why Jochebed sent Miriam to watch over Moses instead of doing it herself, why Jochebed let him go in the first place, and what exactly her role was after Moses was found by Pharaoh's daughter. The fan fic possibilities are endless.
Miriam may be a main player in modern adaptations, but her role in the text is pretty simple. She watches over Moses when he's a baby, gets him back to his mother (2:8-10), and eventually leads the women in dancing when the Israelites cross the Red Sea (15:20).
She gets more screen time in The Prince of Egypt than she does in Exodus. And hey, depending on your tastes, that might be quite all right with you.
Gershom and Moses's Sons
Moses's sons also don't get much screen time. We just know that they exist and that their names are Gershom and Eliezer. Why do you think the Bible skates over these family details? After all, when we elect politicians, their families are totally scrutinized. What do you think? Why does the Bible consider these details unimportant?