It seems obvious to me that your son is wanting his grandparents to realize he's a big kid now and needs his own space. I would talk with him about this possibility and brainstorm with him how he can get out of the "corner" they've put him in. He probably won't have any sophisticated ideas but he gets to be a part of the solution.
I would ask him to come to you when he's feeling out of control or when he's feeling anxious. Use words he understands. I would also watch for early signs of distress and intervene. Perhaps say to the grandparents, I see that our son is not wanting to play a game now. Let's try just leaving him to himself while all of us have a cup of coffee. I think another mother made this suggestion also.
When an opening comes available for a longer talk (without your son being present) suggest to them that both kids and adults don't like to be followed around so closely and told what to do. "Lets try giving him more space. He's more likely to want to be with you when he's able to make choices."
Explain the rules of your house and ask them to follow them. Perhaps give them a copy. Ask them what they expected from their son's grandparents. HOpefully this will start a dialogue that will lead to a solution that everyone is willing to try.
An all together different solution would be for you to plan your son's activities before the grandparents come over. Perhaps feed him dinner before the rest of you eat. Tell the grandparents that the next 15 minutes are quite time and take your son to his room or playroom and get him started on something. When you think he's able to play a game suggest one that you know he likes.
You can enlarge on reasons for what you do. Perhaps even say our son gets so excited when you come over that he needs to have some quiet time to calm down.
How do you get along with the grandparents otherwise? Could you go out for coffee and have a chat with them. This would be more effective if their son, your husband, could also go and back you up if he's not able to handle the conversation himself.
I know that there are parenting books that deal with the issue of children acting out when they are overwhelmed. Perhaps you could find one at the library and ask your husband to read it.
Another idea is to get the book, Love and Logic for Grandparents. It's been several years since I read it but it seems that they covered at least part of this issue. I know it helped me to realize that I needed to acknowledge to myself that I was doing things that made my daughter feel that I'd taken over. Sure seems to me that the grandparents do take over which is causing some of your tension. They are not acknowledging by their actions that you are the mother therefore you and your husband set the rules.
I suspect your husband fears that his parents will not listen to him. He's been told all of his life to obey his parents. They are in charge. But they aren't anymore. He's an adult and in charge of his own life.
It is more difficult to act as the person in charge when your spouse doesn't back you.
I suggest some short term counseling to get past this sense that he has to please his parents. And give him the sense that the two of you are a team. In a way it's like raising children. Disagreements are handled out of the hearing of the children. He doesn't have to agree with you in private. However, his role is to support you when you are with his parents.
Does your husband spend enough time with your son to understand what is happening? Perhaps he's not intuitive and wouldn't notice even if he was doing a part of the caretaking.
Find ways to support him and his beliefs while also asking him to support yours. (in private) Take away the concept that only one person is right thinking and find a compromise.
Perhaps your husband could play with your son with the grandparents. Your son may be more willing to play if he's being held by someone he knows will protect him from losing himself (ie. overwhelmed)
As difficult it will be, try not to be concerned about what others in your family will believe. If you're close to them and they have children they'll see for themselves that your child is good. When you defend your son to them it feels like there may be something wrong. Somewhat like the saying, "he does protest to much." meaning it's human nature to be defensive when they feel threatened. By protesting you are saying that you're not confident enough in yourself and your son to just let it go. You know you're OK so let what other's think be of no concern.
I think I've made some assumptions about some things that if they were different I'd suggest something else.
My assumptions: the grandparent's visit often.
That you have been able to discuss other important issues with them. Perhaps not personal issues but things like politics so that you feel like a respected adult.
And that you and your husband know how to show a united front thru experiences with other issues other people.
If they don't come often, say 2-3 times/year I might just let it slide. If you've never been able to have an adult to adult conversation with them don't start out with an issue that is this important to you and your son. And if your husband is the sort who either let's you handle your social life or argues with you in front of other people you need to work on that relationship first.
Real life example. My grandparents didn't want my dad to marry my mother. My dad was the passive don't make waves sort of person and relied on my mother to fight his battles for him. He did stay out of the way and agreed with her in private.
They lived with my dad's folks when their farm failed even tho my mother and grandparents had a difficult time talking with each other and my dad wouldn't step in. After I was born, the first child, my grandmother doted on me and thought she knew best about caring for me. I remember them arguing over me while I was in the crib. I was less than 2 so I don't remember words or the cause of the argument.
As I grew older I realized that my grandparents were often judgemental of my mother and sometimes would tell their son how he should handle life. I saw my father look at them while they were talking but not really listening. He did nod his head as if he agreed.
My father left it up to my mother to deal with the disagreements on her own. This did not work! They thought my father was hen pecked when he wasn't. He definitely had a mind of his own and made all the decisions the first few years of their marriage. He just didn't want to confront his parents. The result was that my mother became bitter about his lack of active support. She seemed to understand my grandparents and did not stay angry with them but she was still angry with Dad for years and years. I don't think they ever were able to resolve my mother feeling unprotected by my dad. This is grossly over simplified. I tell the story because it illustrates how important it is for couples to have a close accepting relationship between themselves. And that it is best for the child of the parents with whom you are dealing to take the initiative and talk with his parents. If he's not able to do that he must give his wife active support so that the grandparents' words and actions don't negatively affect the parents' relationship.
