While it is true that George Murchison and Joseph Asagai are not the primary players in Lorraine Hansberry's A Raisin in the Sun, they are certainly important characters in the play. The play is set in the pre-civil rights 1950s in Chicago, where racial divides and racial tensions were prevalent and powerful. The Youngers represent blacks at that time, and the same is true of George and Joseph.
Lena Younger is connected both to the old world and the new world. She is old enough to know that things are better now, but she is also quite aware that things are not yet where they should be. She is moved by a fierce desire to keep her family together at all cost.
Walter has become bitter because of his lack of opportunity and advancement. While it would be easy to claim that this was all because of race, we come to understand that part of his problems stem from who he is and not just what color he is. While it is still rather awful to see him suffer, we know by the end of the story that he has been given another opportunity and we have hope that he will take advantage of that.
Ruth Younger is Walter's wife, and she represents the one who is just trying to keep everyone happy amid their trying circumstances. She is willing to work hard, but she knows that her husband is struggling and her son is not getting the life she wants for him. When she discovers she is pregnant, however, she is nearly broken by the weight of her life.
Beneatha is Walter's sister and she represents a different black mentality. She is trying desperately to find her identity as a young black woman. She tries many different hobbies and pursuits, but none of them seem to fit quite right or suit her well enough. She is the one who most identifies with her cultural heritage in this play, and it is Joseph who moves her to this position.
Joseph is a student from Nigeria who presents a contrast to the "assimilationist" position that Beneatha seems to have taken. He is able to make Beneatha proud of her African heritage, something she and her family have clearly not thought much about. Beneatha is intrigued by him and finds herself drawn to her heritage. Josephs is amused by how they met:
You came up to me and you said… "Mr. Asagai – I want very much to talk with you. About Africa. You see, Mr. Asagai, I am looking for my identity!"
His presence in the play is a reminder that blacks have to make a deliberate choice to either seek out and then embrace their heritage or put it behind them and try to "fit in" (assimilate) with the white culture. Because of him, Beneatha chooses to let her her go natural rather than straighten it. Because of him, she wears a tribal robe and dances to authentic African music. She does not do these things all the time, but because of Joseph she is encouraged to be more intentional about the identity she chooses for herself.
In contrast, George Murchison is the quintessential assimilationist black man. He comes from a prosperous (though still middle-class) family and has absolutely no interest in looking back at or embracing his cultural heritage. He has embraced the predominantly white culture, undoubtedly because it has made his family prosperous. He represents assimilation.
These two men are Beneatha's suitors, and choosing between them is literally a choice for Beneatha between embracing her culture or becoming part of the current culture. Without them in the play, these choices still exist; however, they are not as evident to the audience or to Beneatha.