Do you think parents should treat their biological children and step-children the same way? Do you believe it’s fair to expect they’d provide them with the same amount of love, no matter the history?
If you ask me, these questions cannot be answered with a simple yes or no. When two people start a relationship while each of them has kids of their own from a previous relationship, the family dynamic that forms is quite a complicated one. The kids in this family already have their own parents, and they are now being introduced to a step-parent who is basically a stranger to them. The parents are obviously biased towards their own children, but they still want to have healthy relationships with the kids they are welcoming into their family unit. Who can say what should or should not happen within this family? Who can decide if there is one right path to building these types of families?
That is why I don’t think we can expect anything from anyone in this situation, even if it leads to problems with favoritism, like what happened in the story below.