7. Perfect Marriage Revenge- FL turned to be the real daughter of her father and her sister turned out to be a stepdaughter for him. Adoptive mother turned out to be a stepmother for FL. So, this fits
Does Brave Yong Soo Jeong fit the topic description of wicked stepmother and step-siblings? Haven't watched it, but the description doesn't indicate anything like this.
@maidenholmes It is a modern and nice variation. The girl is abandoned with a lady and her daughter when they think the parents are dead. I will not say what happens in the meantime but at the end that lady and that girl are making her the life really impossible when she is 35. It is Cinderella on variations.