The relationship between these two individuals is that they are siblings. Specifically, Katniss is the older sister and Prim, the younger sister. Katniss is clearly very protective over Prim and wants nothing but the best that their limited resources can give her. She volunteered in her sister's place to keep her from harm and to keep her an innocent and young for as long as possible. These sisters love each other very much and that is plainly visible in their actions, attitudes, thoughts, and concerns.
Probably how to prepare for college or job interviews- they're going to go into college next and get a job soon. They don't need to think so far ahead into retirement or getting a house yet. Jet engines sound kind of odd in this category too.
