Hello and welcome *hugs*
you could have a look here for a few thoughts:
https://www.susans.org/forums/index.php/topic,184920.msg1644403.html#msg1644403Know you are not alone in this, and not the only one...
You should see a counselor... preferably a gender therapist, someone who knows the process and can guide you along the way... and they might help explain to parents...
no matter if you ask at plannedparenthood for example, at a lgbt center, or talk to your school counselor for a referral,
or say at home you want some counseling for emotional issues, and pick someone who has, amongst others, gender on their list...
if its connected with depression or emotional issues it might be covered...
they all should keep it confidential if you say so, and are there to help... if you feel someone is not helpful, just look for another...
Well its up to you what you say at home, and if, since you know them best...
talking in a relaxed manner might help... remaining calm and stating facts and a few needs...
one possibility would be to sit them down and talk to them... over a cup of tea... and really talk about your feelings, what moves you... staying in a relaxed tone, not making reproaches but stating your needs... just talking and asking... imo the NHS brochure might help... saying its biological, so its nobodys fault, not yours or somebodys upbringing, and its most likely not a whim or a phase... talking sensibly but saying what you need... and maybe they need some time to really understand...
they might also talk about their fears... what the neighbors might say... (there are many trans people now so more and more people get used to it slowly...)
that she had some fixed ideas about your future... well you are essentially the same person, like a male twin, with the same sense of humour... kids are possible via adoption, or possibly via stopping of hrt for some time... etc...
well as said its up to you what you say... you might think about talking to a counselor first...
Well there are many transgender people now... and people are becoming more and more versatile, some women being more assertive and some wearing mens clothes... men showing emotions... its not like parents grew up... and there might be other transgender people, in groups, at a gsa, etc...
this all is a process, but many have gone it before and succeeded, and people here will try to support you.
And you might keep asking questions, alone writing might help getting a better view...

hugs