Stepfamily Realities 20 & 21 - Stepparent Authority
Even if their bioparents agree that a stepparent has authority to discipline them, stepkids may not agree. Unless they're very young, typical stepkids feel the new adult has to earn the right to tell them what to do. Also, the child's other bioparent or key bio-relatives may not acknowledge the stepparent's authority, and/or may dislike the step-parent's disciplinary "style" (lax <> harsh; consistent <> inconsistent). This is likely if any adult discounts or rejects their identity as a multi-home stepfamily. All these cause significant loyalty conflicts and relationship triangles, which can promote the child/ren to resist and/or "get depressed."
Ideally, the will do most child discipline for months after re/marriage or cohabiting, until the stepparent and stepkid/s have grown some mutual trust and respect. One source of respect is the stepparent firmly asserting her or his rights (boundaries) as a dignified person. A stepparent imposing new rules and consequences on a stepchild "too soon" usually causes resentment, anger, and resistance. Waiting too long may prevent or lose the stepchild's respect, giving them the feeling the adult is wimpy or powerless. One of many new-stepfamily tasks is all co-parents negotiating (a) what a stepparent is responsible for, and (b) how and when s/he assumes caregiving respon-sibilities and authority.
If it isn't practical to go slowly, it helps if the bioparents "authorize" the stepparent in front of their stepkids, like: "Melissa, if Jerry tells you to do something, it's just like I'm telling you...".Some experts recommend that stepparents act like aunts or uncles for some months, until enough co-parental respect, trust, and authority are earned.