Lyra gets away along with her daughter and ends up leaving Saw's group for a different branch of the Rebel Alliance. Cassian says, "I've been in this fight since I was six years old"... So they grow up together. And it's not all puppies and fluff, it's a tough upbringing, but it's made better because they have each other.

+ Cassian is the only one outside of the family that knows their relation to Galen Erso. Until plot happens.
++ Lyra treats Cassian like a son.
+++ Lyra ends up killing Krennic.
++++ Jyn and Cassian are each other's first kiss or first time, but not both.