There is a good reason to improve difficult family relationships: It has a big influence on your mood. And your mood has a big influence on the moods of people you know, and affects your health.
You might think I'm going to recommend forgiveness and forgetting slights. I will recommend nothing of the sort. The surest way to improve difficult family relationships with with honesty. But it has to be done a certain way. Find the key here: Attitudes and Kin.