Grandparents don't necessarily do anything wrong to be denied access - they are useful pawns to hurt when one parent or the other wants to wreak revenge or exert control.
The posts are not too long - we all have the freedom to write as long or short a post as we want - readers have the choice to read or not.
Inbetween in your post you say:
'.....sunday dinner it has been accepted once where they then continued to moan about the cooking little did they know it was my partners cooking and they tought him! So he was very upset that day. '
I don't understand why you wouldn't say that your partner had cooked the dinner? Why be upset in your own home and not feel able to assert yourselves, or make a joke? I would have said 'don't you be pulling your face at the cooking when you taught him to make this lovely food ha ha!'
How has it come to this, that you are all treading on eggshells round each other, and engaging in games, instead of you being open and honest and giving them an opportunity to apologise and start correcting the mess it's turning into? Have you thought that they may be as confused and upset as you are? It comes to something when you are interpreting their behaviour because they have left an open newspaper to send you a message about court.
If they won't engage in a discussion, send them a reasonable letter, setting out what you need from them and clarifying the boundaries. They'll probably retreat to lick their wounds, but if they really want to see their grandchildren, they'll grit their teeth and crack on with getting it right before they get much older.