how do i tell my parents my partner is trans?

so recently, my beautiful amazing girlfriend came out as transgender and is intending on starting hrt soon!!

one thing im rlly worried about tho, is telling my parents that she is going to be transitioning...

for context:

ever since meeting my parents, she has occassionally worn feminine clothing such as skirts and dresses to my house. so my parents atleast have an idea of her being a "feminine dude."

what is atleast a little promising, is that my parents absolutely love & trust her! and both of my parents are mostly aligned with left-wing ideologies. but the issue is, i have no concrete understanding of how they stand with lgbtq, and more specifically transgender individuals.. and something important to note is that they don't know any lgbtq people personally.

im a bit worried... because they have already made several comments about my gf wearing a skirt. my mum mostly just laughs about it and asked me if she was 'one of those nonbinaries' (while laughing). with my dad, he hasn't said anything to my face. he apparently just simultaneously defends her decision to wear skirts & jokes about how she wears them. plus, he has made jokes about pronouns in the past.

the most innocent interpretation of their behaviour is that: they just know nothing meaningful about transgender people and view it as weird & foreign (due to their lack of exposure) but dont have any strong hatred towards the group. but i cannot be sure, and their current behaviour is a tad concerning.

anyways, the question i have is: how do i go about telling my parents that my partner is no longer my boyfriend anymore, and that she is transitioning to female? my main goal is to get my parents to understand and respect her. (additional context, she currently doesn't mind he/him pronouns)

more specifically, how do you begin the conversation? how do you educate your parents without provoking them or making them defensive? and also, how do you stay calm in this situation?

i would rlly appreciate hearing anybodies advice or experience with this situation, it would help me tons <3

many thanks!