All the observations may be true. There may be behavior problems, but the harder the stepparent comes on with new rules, the more deeply he or she will drive a wedge into family relationships. Over time the stepparent can expect to have more influence. But communication with the spouse is essential. With teen-agers, stepparents may never reach the level of authority held by natural parents.
Stepparents help create family unity when they Work with the natural parent.
Communicate as husband and wife, apart from the children, about all rules and routines. Find out the background of family rules, procedures, and activities. Let the natural parent verbalize rules and hand out consequences in the beginning. Consider both spouses' feelings when communicating about the rules. Allow time for a real feeling of family to develop.