Mariam is a true hero, sacrificing herself to save her friend and the children she's come to love. If she has flaws, they are hard to find. Mariam is dealt a rotten hand in her childhood, abandoned by pretty much everyone, and forced to marry a rotten man because her biological father really doesn't want to deal with her. She is fairly resigned to living a life of solitude when Laila drops into her life. Granted, adjusting to having a second wife in the house isn't what women dream of, and Mariam takes a while to find peace with this new situation. Eventually, though, she comes to be Laila's devoted friend and loyal protector, killing Rasheed when he threatens to kill Laila. Because of Mariam's sacrifice, Laila can live and even work toward making Afghanistan a better society.
On the other end of the spectrum, Rasheed doesn't have a redeeming quality to note. Rasheed believes that he has the right to physically and sexually abuse the women in his house, and he lies to Laila for a long time about the true fate of Tariq in order to further manipulate her. He marries Mariam because he expects children from her, and when she can't deliver on this expectation, he casts her aside, offering her no kindness as she basically becomes a shadow of a wife in their home. It might be tempting to feel compassion for him because of the loss of another son who drowned—but only if he had any moments of tenderness or kindness. Unfortunately, he really just seems evil to the core.
A character who might fall somewhere in the middle would be Laila's mother, Fariba. When we are presented with a younger version of Fariba, whom Mariam meets when she's younger, Fariba is compassionate and loving. Yet the woman who is Laila's mother when the action picks up with Laila's story is distant, cold, and unbelievably grief-stricken. Because she grieves for her sons, she can't be the mother Laila needs, and that tension is difficult to completely forgive, even in light of her circumstances. Yet it's impossible to blame her for feeling such profound grief. Thus, the reader finds it easy to both sympathize with Fariba and long for her to find the resolve to be a source of support for Laila, another young woman desperately in need of guidance in their restrictive society.
I hope that helps you get a handle on how to begin classifying some of the characters. Others you'll want to consider are Laila, Tariq, Laila's father, and Mariam's father. Good luck!