Well, I’m no expert, but if I were ftm trans and wanted to come out here’s how I’d say it:
Call your parents to talk to you about a serious topic
Say this: “So, I’ve been thinking about this for a long time, and I have decided that I now identify as a man. I hope you will let me dress masculine, and refer to me as a male. Even if you don’t agree with me, please respect my decision.”
If they accept you, great!
If they don’t, sad, but you tried!