QUESTION: My son has two young children and a few years ago married a woman who has two children of her own.My son and his wife are having some financial troubles and my wife and I have volunteered to help them out with baby-sitting whenever they need it, which is quite often.My son’s children are pretty well-behaved when they come to my house. They help set and clear the table, say “please” and “thank you,” participate in mealtime conversations, and so on. They’re not perfect, but who is?My daughter-in-law’s kids are a different story. They’re rude, disrespectful, refuse to help out, criticize the food we prepare for them, and generally act like they’re living in a hotel.It’s gotten so bad that I’m about to tell my daughter-in-law that her children are no longer welcome in my house, but I’m afraid that might end up hurting my son’s marriage. His wife truly believes her children can do no wrong. What should we do?ANSWER: Ah, welcome to the wonderful world of grandparenting in the age of blended families. You’re absolutely right to worry about throwing a wrench into your son’s marriage. But you also need to be concerned about how his stepchildren’s behavior might affect your relationship with him. There’s also a serious risk that as your biological grandchildren see what their stepsiblings get away with, they’ll start imitating them. So you’ve got to put an end to this problem right away. Unfortunately, no single approach will work every time, so here are a number of strategies that will allow you to attack this problem from several angles at once.• Do NOT talk directly to your daughter-in-law, at least not alone. From your description, she’ll just get defensive and will end up painting you as the bad guy. That will put your son in the awful position of being in the middle between you and his wife.• Treat all four children the same. If anything you do comes even remotely close to favoritism, again, you’ll be branded as the bad guy.• Talk directly to all four kids at once. Tell them — without singling anyone out — that there are some behaviors going on that are simply not acceptable and that if things don’t change in a hurry, you’ll make a report to their parents.• Call a family meeting; you, your wife, son, daughter-in-law, and all four kids. Tell them that you have certain rules in your house and that rude, disrespectful behavior will not be tolerated. Ask the kids to create consequences (don’t use the word “punishment”) for breaking the rules. Chances are they’ll come up with things that are harsher than anything you would have. The added bonus is that when they break the rules they won’t be able to gripe about the punishment.• Talk with your son and his wife. Tell them that you often have trouble with the kids and that you need their help establishing some rules. Be very careful that you don’t single out your daughter-in-laws kids. It’s critical that she and your son support you by telling the kids that when they’re in your house, they play by your rules. And that violating those rules will result in serious consequences. This is critical. The kids have to hear from their own parents that you’re the supreme authority in your home.• This one is hard but it has to be done. Tell your son and daughter-in-law that if the behavior doesn’t stop, they will have to make other child care arrangements.Armin Brott is the author of “The Military Father: A Hands-on Guide for Deployed Dads” and “The Expectant Father: Facts, Tips, and Advice for Dads-to-Be.” Readers may visit his website at www.mrdad.com.