Values are what bring distinction to your life. You don't find them, you choose them. And when you do, you're on the path to fulfillment.
The above sounds like someone trying to justify behavior that there is no justification for. I am not talking about petty differences here. I don't think anyone ends relationships over anything petty, ever.
Marriage is the primary commitment after God. Parenting your child is a right. Your relationship with your grandchildren is a privilege not a right. When your parenting or your spousal relationship is being undermined this is crossing a serious boundary. When these two things conflict greatly and one has to end as a result, it should be the in laws.
It is not only the right thing to do but your responsibility to cut evil people from your life. Some things you don't come back from.
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