Q: My husband and I have a “yours, mine and ours” family. Six months ago my husband’s oldest daughter, age 17, decided to come live with us. It has been hard on our marriage, our other children, his relationship with his ex, my relationship with his ex — and everyone is up in arms. He will not set boundaries for either of his daughters, but the oldest one has broken every house rule we have so we sent her back to live with her mother.

Mother couldn’t handle her, either, so she’s back at our home. She tries to manipulate everyone. I can’t do this anymore. She goes or I go, but I don’t want to be without him. What’s good ex-etiquette?

A: You probably feel as if you are between a rock and a hard place. Truth is, you’re not. Here’s the problem: People who combine families often think the basis on which a family is designed is different now that they are no longer a conventional family.

But, a breakup does not undermine the need for children to have structure. They need role models, and even though you are not this child’s biological parent, watching how you and Dad establish house rules and respect each other as the primary relationship in your home is exactly what has to be done to offer these children security. Take that, integrate it with respect for the other biological parent and their input, and you have a recipe for success.

So, what’s going on at your house? What I am hearing is that Dad has lost his way and he’s afraid to call his oldest daughter on her bad behavior — possibly out of guilt or possibly out of, “I might never see her again if I make her mad” — but she’s challenging Dad and he’s keeling over, and you’re left feeling abandoned while the child’s mother is left feeling powerless.

Normally, I talk a lot about Ex-etiquette for parents rule No. 1, “Put the children first.” But in your case, in order to put the children first, Dad must make it openly oblivious that every decision for his daughter that is made in his home has been discussed with her mother and that you are on the same page supporting Mom and Dad. When she realizes that all the parent figures are on the same page, her manipulative behavior will stop.

Finally, if Dad’s indecision is propelled by guilt, he has to get over it. Feeling guilty and giving in to a child who is searching for her way is doing her a disservice. She needs strong boundaries and role models. She needs to understand that although she is almost an adult, that’s an arbitrary number. She needs to know she can depend on the parent figures in her life to help her make good choices.

If she’s running the show, there’s no one for her to look up to. She needs a hero. I bet if the adults in her life put their heads together they will be able to find one — or three.

Jann Blackstone is the founder of bonusfamilies.com.