Why should I express my emotions in a family relationship?
Sooner is easier
A lot of people don't, because it's your family! however, the more and longer you repress your feelings, the more likely these emotions will eventually explode in a way that's even harder to manage or recover from (both for you and your family).
Expressing your emotions can also help your family member(s) to understand or at least be aware of what are the "triggers" for you.