It really depends on what kind of relationship you have with your family members and what kind of people they are.
You only have to read the coming out stories here to see the vast range of possible reactions. Coming out is all about managing the reactions. If we didn't have to consider reactions, coming out would be easy: you'd just tell them, and if they had a problem with it, drop them. But we can't easily drop family, so we have to take into account how they will react.
When coming out, plan ahead how you think they are most likely to react. Since you often can't predict their reactions, consider a range of possibilities. If you think that the reaction might be abusive, plan for your own safety: that may be a situation where a phone call or email might be better than telling them in person.
If the person is someone you do not need in your life, their reaction is less important. If they are important in your life , you will need to anticipate any problems they may have and try to soften the blow by including information that might help them react more favourably.
My two brothers are the only family I have. I'd like to keep them in my life if I can, though I could live without them if my safety was at risk. Both live far away, so I told them by email. One brother I knew would be accepting and supportive, so I just said, "Surprise! This is my coming-out letter. No, I'm not gay, I am transgender."
The other brother, I was much less certain about. In fact, I expected a negative response. So, I wrote a longer letter, explaining a bit about my personal history, then explaining about the science behind being trans, before I even mentioned the T-word. I wanted to be sure to cover that this was a medical condition, that it was not a choice, and that my treatment was medically-supervised in response to a diagnosis. As it turned out, he was supportive after all. Hope for the best, plan for the worst.
With a spouse, the stakes are higher. I knew I had to tell her first, and that I had to tell her face-to-face. Again, I had to plan for the worst. "Worst" looked to be pretty bad, and it took me monthe to build up the courage to tell her. But, eventually, I was prepared to accept "worst" if it happened. It turned out that she became my biggest supporter.
Hope for the best, plan for the worst.