Lena and Ruth represent the stereotypical female role of the past; this is part of the reason that there is so much tension between the two women and Walter and Beneatha.
1. Lena is the matriarch of the family and represents the circumstances that many older mothers of the 50s faced. She is a relatively young widow; she must still work in order to be able to provide for her adult children, and she maintains quite a bit of authority over her children--mainly because they still live with her. Specifically in the play, Lena brings hope, common sense, and history to her family. She still dreams that she might have a house for her family even though she finds herself late in life. When Walter gets riled up, she attempts to calm him down; when Beneatha flits from one interest to another, she counsels her to be stable, and when Ruth sees her new baby only as an obstacle, she reminds her of the blessing of new life. Most significantly, Lena is able to remind her children of the past, not just what their father went through but also of the values that their culture once adhered to so strongly. She admonishes Walter in Act 1, Scene 2,
"Oh—So now it's life. Money is life. Once upon a time freedom used to be life—now it's money. I guess the world really do change . . ."
2. Ruth also fits a certain stereotype of her day. She desires to be a supportive wife to her husband and a loving but strict mother to her child. Her relationship with Travis somewhat mirrors Lena's with Walter. While Ruth is not much older than Beneatha, she clings to tradition and a sense of identity through her husband. In contrast, Beneatha is the modern woman--independent, open-minded, and bold. Ruth's role is not significantly different from Lena's. I think that Hansberry characterizes Ruth in such a fashion to demonstrate that traditional female roles and modern ones will always clash.