I am going to marry my boyfriend soon, and suddenly I heard that his family is going to move his father's grave.

You're getting married. Have you discussed it with your family beforehand? Since you want to be a member of their family, think about your family first, so that the man's parents will agree with you and think that you are an ordinary person and will get along more harmoniously in the future. Secondly, marriage is just a form. What does it matter if two people get married sooner or later? Moving before marriage is good for you.