Not to frighten you, but here's my story:
I was sitting in my parent's living room with my mom, dad, and my wife. I told them to turn the TV off, I had something I wanted to talk about. So I told them. My mom sat there in silence, wishing she was dead, while my dad berated me. So me and my wife got up and left and went home. I cried for a couple days over that. My dad wrote me a very nasty letter disowning me.
That was 2 months ago, and my mom has her fingers in her ears going, "Lalalalalala." She won't seek any help (therapy, counseling, support groups, etc...), in fact she blatantly refuses to do so and says that she has no plans or desire to do so (she told me that today actually). I'm OK with my dad's reaction, but my mom and I have been close all my life, so I'm hoping she gets on board eventually. This train is leaving the station with or without her. Me and my wife live 100 miles away from them, and have for the past 7 years, so they're not stopping me either.
So anyways. Telling them face to face is the band-aid approach. I am all for it, but just be prepared for all possible reactions.