Wiki article on this topic: A stepmother is the current wife of one's natural parent that is not one's biological mother. A stepmother-in-law is the step-mother of one's spouse and the wife of one's father-in-law or mother-in-law. The children of the step mother-in-law would be the person's step brothers-in-law and step sisters-in-law.
Step parents may also face some societal challenges due to the stigma surrounding the "evil stepmother" character. Morello notes that the introduction of the "evil step-mother" character in the past is problematic to stepparents today, as it has created a stigma towards stepmothers. The presence of this stigma can have a powerful, negative impact on stepmothers' self-esteems according to one Christian study.
In fiction, stepmothers are often portrayed as being wicked and evil. The character of the wicked stepmother features heavily in fairy tales; the most famous examples are Cinderella, Snow White, and Hansel and Gretel. Stepdaughters are her most common victim, and then stepdaughter/stepson pairs, but stepsons also are victims as in The Juniper Tree—sometimes, as in East of the Sun and West of the Moon, because he refused to marry his stepsister as she wished, or, indeed, they may make their stepdaughters-in-law their victims, as in The Boys with the Golden Stars. In some fairy tales, such as Giambattista Basile's La Gatta Cennerentola or the Danish Green Knight, the stepmother wins the marriage by ingratiating herself with the stepdaughter, and once she obtains it, becomes cruel.
In some fairy tales, the stepdaughter's escape by marrying does not free her from her stepmother. After the birth of the stepdaughter's first child, the stepmother may attempt to murder the new mother and replace her with her own daughter—thus making her the stepmother to the next generation. Such a replacement occurs in The Wonderful Birch, Brother and Sister, and The Three Little Men in the Wood; only by foiling the stepmother's plot , is the story brought to a happy ending. In the Korean Folktale Janghwa Hongryeon jeon, the stepmother kills her own stepdaughters.