How to deal with family holidays when grandparents don't believe in ADHD?

My parents are coming for the holidays and they plan to stay for a week. We have two boys with ADHD and my parents don't believe ADHD is a real issue. They think we are bad parents and tell us we should control our kids better. Our boys (6 and 9) are active but they are not wild. They both take medication to manage their symptoms which upsets my parents who think they should be able to be calm without it. I am bracing myself because I know they will have lots of comments about our parenting while they are staying with us for a week. Any help you can offer is appreciated because I don't want their to be any big disagreements while they are here. What do I do if they criticize our parenting?