How I hope to tell my family about my Engagement...

My boyfriend and I are engaged we are both 19 and I hope to tell my family especially my parents through Facebook I just feel like they won't understand if I told them in person and just say "You're too young" and scold and lecture me. My man and I have been together for 3 years but we have known each other for 5 we started off as really great friends to BF and GF and when I told my friends of my idea some agreed and some not so much my best friend said I should get my BF to ask for my father's blessing which kind of pissed me off I'm sorry but I believe in equality and asking someone to marry their daughter is so old schooled and sort of sexist if you go back in time far enough so I will not be allowing that to happen but still I just don't know if the just posting it to Facebook without warning is a good idea or not...