Living in a blended family takes time and readjustment for everybody concerned. Teenagers, in particular, can find it difficult to cope with a new family setup. They haven't chosen to have a new stepparent and may have to cope with feelings of jealousy and anger. Sometimes they might have to move into the stepparent's house. If the stepparent also has teenage children, then the blended family has additional challenges to face. Love and patience are essential to make sure the blended family is successful.
Give everyone in the new blended family space to adjust to the new situation and the new personalities. Do not expect to create a perfect, smiling family overnight as relationships take time to build.
Include the whole family, including the teenagers, in family decisions to promote cohesion and involvement. Consider establishing regular family meetings where everyone can discuss their feelings and concerns.
Set aside some family time each week so that everyone can get to know each other in a fun situation. This could be as simple as a games night or playing a sport together.
Give the biological parent the main disciplinary role initially. Once the new stepparent and teenagers have established a bond, the couple must then present a united front in terms of discipline and boundaries. All children, including teenagers, try to play one parent against the other to get their own way.
Accept attitude and mood swings while the teenagers adjust to the new blended family. With time the teenagers might thrive and flourish in the new setup.