Q. My co-parent and I have two kids. I recently married a woman with two more children, a few years younger than my own. My wife insists on going to the children’s doctor and dentist appointments, which causes my co-parent to become extremely territorial and recently caused a huge brouhaha at the dentist’s office. The kids were there, and the receptionist threatened to call the police if things didn’t calm down. My wife still insists on going even after all that. She thinks she‘s completely in the right and it’s my ex’s problem. What’s good ex-etiquette?

A. Have to say it, your wife’s out of line.

Ex Etiquette Rule No. 4, “Bioparents make the rules, bonus parents uphold them,” makes it very clear: Bonus parents should not interfere in an already established co-parenting plan — unless, of course, he or she has children of their own in the home. Then it’s a carefully orchestrated dance combining past and present rules using all the kids as the criteria for decisions.

Better that your wife works on building a cordial rapport with your co-parent so they can keep communication open and problem solve in the best interest of the children.

If not, you see what happens: Mom gets offended and feels that bonus mom is overstepping her bounds, which, quite frankly, she is. Unless your wife’s children have appointments on the same day and at the same office, there’s no reason your wife should attend your children’s appointments unless she’s asked to attend.

Parents who are no longer regarded as a couple often feel guilty that they can’t be with their kids. Add to that an overzealous bonus parent trying to take over parental duties and that’s asking for trouble.

It helps if each parent and bonus parent finds their niche — what can either do well and offer that to the kids? Or, if parent figures must share responsibilities, like homework, for example, look for ways to cooperate so that the kids have people to emulate. That’s good ex-etiquette.

Dr. Jann Blackstone is the author of “Ex-etiquette for Parents: Good Behavior After Divorce or Separation,” and the founder of Bonus Families, bonusfamilies.com. /Tribune News Service