The fuller answer
Blended families combine people with different histories, rules, losses, loyalties, routines, and expectations. A new partner or stepsibling does not instantly feel like a parent or sibling because adults chose a relationship.
Young people may feel displaced, watched, pressured to be happy, or guilty for liking a stepparent. They may protect the absent parent by rejecting the new family, or fear that closeness means replacement.
Healthy blending respects time, privacy, existing relationships, and clear adult responsibility. Children should not be used as messengers, spies, or judges in adult conflict.