My parents live several states and hundreds of miles away, which is how I like it for the most part. We're not as close as most people tend to be, because they're not the ones who really raised me, so it's complicated but we're not estranged either.
Mother knows something is different about me, I told her over the phone that I was taking testosterone and she's known for a few years now that I identify as a man but I don't think she really, really...gets it. She's not really being stubborn or mean about it or anything, it's just like it goes in one ear and out the other.
For Christmas I was thinking about telling her I finally got around to getting my GED, and also a little note or letter explaining more details of the trans thing, but I'm just not that emotional. So it would probably be like, "Oh yeah. I'm not the most emotional person around, so you'll have to forgive me if this sounds a little cold. I'm taking testosterone. I can grow a beard. My voice is deep. Yes, I'm cutting the boobs off. Yes, I will run around shirtless at the beach. Yes, I go in the men's bathroom. So in the future, please keep in mind that I will look and be treated as a man by the public. If you continue to call me a girl, that's fine, but I will not go out in public with you."
I'm not stupid, I know how cold that sounds, but I just don't think it would do me any good to sugar coat it. Mother will probably cry and try to get over it, but my stepfather (only of five years or so) is a black man with an entirely different attitude. He doesn't sag his pants or anything but he's still a little thug and macho. I don't have a clue how he will handle it.
I wrote a letter to my parents. That way I could keep my distance until they had time to process. I thought my dad would be cool and my mom would cut me off. Turns off my mom is really supportive and my dad is having problems with it. I mean, I speculated for months and still couldn't predict that. All this to say, your parents may surprise you.
I was positive my dad would disown me, but him and my stepmom have been incredibly supportive. They have all 3 of my stepsisters using the correct name and pronouns after only a few weeks of being out to them.
I say, state your business in whatever way you think they need to hear it (blunt, informative, or emotionally if need be). Know that their emotions are their own and there will be little you can do to immediately do anything about them. Be prepared for the worst, whatever that may be for you. Ultimately you've gotta do you and they've gotta decide for themselves what that means to them.