4. Don't react. Emotional bullies and other people who seem to strive to make you feel uncomfortable do it because they can tell by your reaction that they are successful in making you feel off balance. When you give a reaction to their attempts, they see it as they "got you." In short, your reaction reinforces their behavior.
5. Choose to "opt out." If you and your partner have tried your best to remedy your in-law situation and they continue to be unbearable, consider the option to "opt out." There will always be some people who will find their own agendas more important than familial harmony. However, just because you're married, you're under no obligation to be emotionally abused by toxic people.
If your partner chooses to see with his parents, let him. They are after all, his parents. Take the time he wants to spend with his family and do something to nurture yourself — or better yet, spend the day with people who treat you right.