Here's what I'd suggest: If your soon-to-be holiday houseguests live close by, ask them individually to meet you for tea or coffee before the big event. If distance prevents this, ask them if they can talk with you by phone at a time when they won't be rushed. Let them know that you are anxious about the upcoming holiday housewarming, and you need their help and understanding. Tell them that you know that they (or other family members) may not believe that your son has ADHD, or that they may believe it, but they may feel that you and your husband aren't doing what your son needs. Let them know that you want them to have a better understanding of not only ADHD, but of the kinds of things you and your family have done to try to create the best environment for your son. Tell them about the program that he's in at school. Tell them about the behavioral strategies that you and your husband have learned to help you work with your son at home. If you think it's appropriate, tell them about medication he may be taking or the other treatments he's involved in.
Let them know that the hardest times for your son are transitions and big exciting events, like the one you're having. Tell them you are going to need their help in calming things down from time to time. Ask them to spend some individual time with him while they are there, so that they can appreciate his talents and see his positive side. If they need help coming up with an idea, you can help them plan an activity that will help him be more successful and in control when he is with them. Something as simple as a short walk or making a snow-angel will work well.
Your relatives need to understand that the ADHD provides an explanation for some of his behavior, but that neither you nor his teachers ever allow it to be an excuse for inappropriate behavior. Suggest that your relatives read a good book on ADHD, such as A Parent's Guide: Attention Deficit Hyperactivity Disorder in Children by Sam Goldstein, Ph.D. and Michael Goldstein, Ph.D. You may also want to give or send them a copy of the excellent new videotape by Russell A. Barkley, Ph.D.entitled A New Look at ADHD -- Inhibition, Time, and Self-Control, parent's edition. To help your relatives help their kids understand your son better, you might want to suggest books such as these: Shelley, the Hyperactive Turtle by Deborah Moss (ages 3-7); Jumpin' Johnny Get Back to Work! A Child's Guild to ADHD by Michael Gordon, Ph.D. (ages 5-10); or Zipper, the kid with ADHD by Caroline Janover (ages 8-13).
If you like to write, consider a holiday or New Year's letter to your family (or to certain members of your family). Tell them some of the things that were mentioned above. Do not use this letter to tell them how mad you are, or how disappointed you are. Words, especially in print, have a way of hanging around and showing up later. Focus on what you need from them. Tell them that your wish for the beginning of the next millennium is that they all will have a better understanding of your son, his condition, and it's impact on him, and the entire family. Tell them also that you want them to come to know his gifts and talents, and be able to enjoy him as you do. Ask your family for their love and help. If they can give it, you and your son are fortunate. If they can't or don't know how to respond to you, at least you know you have given them the opportunity.
I wish you well. Let us know how it goes. May your holiday be very special. Enjoy the new house and your son in the new century.