Q: My husband and I share custody of his two young daughters. I also have kids from my prior relationship — one is in middle school and the other in high school. My husband's daughters see their mother every other weekend, so she doesn't have much influence on them, but each time they come home, they are terrible. It takes me days to straighten them out. What's good ex-etiquette?

A: You do know there are all sorts of red flags in your question, and I think you're operating under some major misconceptions.

First, and this will sound sexist, but it's an observation derived from years of experience working with parents and the court system. When a father has primary custody of his "young" daughters, something went on before the breakup that you're overlooking or not mentioning. It could be anything from mom being an executive and traveling to drugs and alcohol, but something is up. I'm not saying that mothers are better parents than fathers, so please don't write me about my observation. However, the truth is, most courts grant mothers, in particular, at least 50 percent custody unless she has openly consented otherwise or there has been a problem. I suspect these kids have dealt with some big things before you came into the picture.

Next, you and your husband don't share custody of his children. He shares custody with their mother. Granted, you play a huge part in their lives, but dad is dad and mom is mom. Thinking otherwise inadvertently forces the kids to take sides.

Which brings us to the next red flag — everyone in these children's lives influences them. If you truly don't believe their mother has an influence on them, you're mistaken. If she didn't, you wouldn't have so much trouble getting them organized when they return. Any child who goes back and forth between their parents faces questions about allegiance and betrayal — and it's increased if they like their parents' new partner.

You also may be subtly negating their mother's importance, and that makes the kids question their allegiance — not to their mother, but to you. Even saying something like, "Why is your mother always so late?" put the kids on notice.

Finally, unless you have a plan to handle the constant intertwinings of children going back and forth between parents, you're going to face transition problems — and the first person to consult if the girls are acting up is their mother. It would not be uncommon for her to want to upset the apple cart at your house if she feels like she is on the outside looking in. Keep her in the loop. The more information she has, the more cooperative she will be, and the kids' transition will be easier as a result.

Jann Blackstone is the author of "Ex-etiquette for Parents: Good Behavior After Divorce or Separation," and the founder of bonusfamilies.com.