5. Remember, your spouse will seem different with his/her family. We all have a role in our family of origin (FOO). When you get together with people you only see once or twice a year, you are expected to play that role. This is true despite the fact that you are now a grown-up and not a sniveling child or adolescent. Chances are, you will see your beloved in that historical role. Don't knock it; it's probably the same in your FOO. Be kind.
6. Remember, not everyone will love you all the time. Borrowing from Albert Ellis' wonderful irrational beliefs, you have to recognize that, unlike your FOO, your in-laws are not obligated to love you. In some families, there's a clear norm for embracing the in-law like a blood relative, whereas in others, not so much. Remember, your self-esteem is not on the line and neither is your relationship. And you're not going to love them all either.
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7. Make it fun. Particularly if you know it's going to be difficult, I like to challenge people to tell me one or two ways to make it fun. Some examples to get you started: Learn something new about someone; give someone the gift of listening to them; make someone laugh; or, set an intention to see the humor in everything.
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Perhaps you've noticed that this is more about managing your reactions to your in-laws during the holidays than about managing them. That's because, unlike your dog, you can't manage your in-laws any more than you can manage your own family. What you can manage are your expectations for them and your reactions to them. You can also manage your stress level by making sure you're engaging in stress management during the holidays. For the ultimate management, consider starting your own rituals as a new family.