Your immediate and extended family can, and hopefully will, be a strong positive influence on your child's growth, development, and moral education. If you are dealing with a defiant child, think carefully about how your family works and simple changes to dynamics that can maximize their positive influences.
You don't have a choice about who your extended family members are. Your parents, siblings, cousins, grandparents, and in-laws are who they are, and you can't change them. Hopefully, they can support you and your efforts to help your child. In order to help them be effective, share what you can with those who need to know first, and do so out of the child's earshot by making a phone call while he's at school or by sending an e-mail. You'll need to let extended family members know if they share caretaking duties or will be coming for an extended visit. For those you see little of and aren't comfortable around, you can keep your child's behavior issues somewhat private.
When it's appropriate, share your observations and strategies with those who need to know. You can ask input from other caregivers, but don't ask permission. When you need to make a mandate, be polite and firm: “Carter is allergic to wheat. Please do not give him wheat or wheat products, like pasta, under any circumstances.” Request that people do not roll their eyes or make fun of your parenting practices in front of your kids. If you don't allow your kids to play videogames as much as their cousins, do not allow your brother and his wife to tease or belittle your kids about it. Do allow grandparents — especially those who don't see your child often — to spoil the child within reason and as long as it is safe.
If your immediate or extended family has toxic behavior patterns or issues you're not comfortable talking to your child about on your own, ask your local library if they have age-appropriate books that can help. Be aware that some libraries keep books on sexuality, abuse, and other sensitive issues behind the desk, so you may need to ask for them.
Finally, when the family gatherings are over, talk about them with your child. “What did you think of your cousin's new tattoo?” “I thought Aunt Sarah seemed tired and grumpy today, what did you think?” and “Wow, Grandma and Grandpa looked pretty excited about their new video camera!” are good conversation openers for the drive or flight home. Ask for your child's opinion and share your own as well.
When you're not happy about someone else's words or actions, use effective communication skills that focus on behaviors and feelings instead of condemning people. Instead of saying, “Your Uncle Dan is a sleazeball,” try, “I'm not comfortable with how Uncle Dan talks about women's bodies. What did you think?” This allows your child to continue loving the family member and to think about the behavior.