It can be annoying when your in-laws give you a hard time but as an adult you learn to deal with it. The thing that can be harder to deal with is when they bring your children into it and try to play you and your children against each other. From the first time they do it you need to mention it to your spouse and hope that his intervention will calm the troubled waters.
Make sure that your children are never exposed to the hurt that they are causing and if necessary keep them away from each other. They may be happy if you no longer go to family engagements but if the grand children do not go there will be a couple of problems caused. Firstly they will not get to spend as much time with their grandchildren as they would like and secondly other family members will comment that the children are not there and ask why – there is not really a good answer to that question from their point of view.
One of the best ways to cope with the attitude you are facing is to learn to know when it is about to start. If the family are having a good day and you feel the atmosphere changing get yourself and your children out of the situation. It may work a bit like the Pavlovs Dog scenario – once they realise what they do has bad consequences for them they may stop. If this is then followed up by a period of time when they in-laws do not get to see their grandchildren or even their son then they may learn to behave in a better way the next time you are all together.
To stop the in-laws interfering in your marriage you do need to keep your spouse on side and even if they do not want to stop seeing their parents they must be prepared to support you when it comes to you and the children seeing them.