In addition to desegregating war industries, president roosevelt agreed to:
a. end discrimination in the military draft.
b. begin desegregating public schools.
c. make better jobs available to african americans.
d. support african americans running for office.

the three roles stated in the dialogue develop the siblings' personalities.

lloyd's personality looks like a trademarketer

dana's personality is afraid from lloyd's behavior and the oldest sister is a decided person who tries to solve any conflict

i believe it would influence their own way of understanding things. it shall be a foundation where they can draw or start an argument.   historians are also  scientists that  have their tools of analysis and expertise to unlock a variety of difficulties such as relationships of man, origin, politics, economy, and culture. based on facts and understanding on these areas, they may shade light to extract ideas and develop options to validate a hypothesis or debunk it.