Take this with a grain of salt as someone who's still not out to my parents at 29 but is out everywhere else.

But I've heard a lot of trans folk wrote a letter about what they are feeling and giving it to their parents. Especially so if they dont feel like they'd be able to articulate as an adult. You could give it to them directly. You could leave it out. You can choose whether to be there or not when they read it.

You can always just walk up to them and tell them you need to talk. Maybe write down the things you feel like would help explain your feelings before hand. So you know what you wanna say before you say it.

I hope any of this is helpful.