I didn't tell them for a long time, as I was afraid of the fallout. The hardest thing I did was tell my kids that I wasn't a member anymore when they asked if I had a testimony.
My parents were just like "Thanks for letting us know." One of my siblings who had already left years earlier reached out to talk about it for the first time.
They "still" love me. I despise that phrase. It implies I've done something wrong. "We love you in spite of that horrible thing you did to leave the tribe."
When I told my father I was mentally out at 17 y/o, his reaction was very negative. I sent my letter, started drinking coffee, and lived my life with little resistance from the mormon point of view. When my brother started to prepare for a mission, I got more defensive about my beliefs, since they were coming up more. Finally, I had a fight with my parents where I explained to them what effect the church has had on my life. They felt sorry and didn't realize that that was my experience. It's not their fault, they were just doing what they believed was right. I am free to be non-religious around them now, and things are okay. I am VERY, VERY lucky, I know this.
As with probably most families, their reactions were as unique as the family members themselves. One family member was very angry, and I had a 2-3 hour long heated argument with them about my denouncing the faith. Another family member actively encouraged their spouse to not discuss my faith transition with them. A different family member now avoids discussion religion while I'm around, and yet a different family member loves bringing it up at every turn, as if in an effort to reconvert me. A couple others have been indifferent about the whole situation, and another will make snide comments and remarks about my current life choices at any opportunity they get. One family member is a closeted nonbeliever, and shares links with me, asks questions about my transition, and so forth. So, it varies. For the most part though, family gatherings are just fine. It's not uncomfortable to hang out with my family, and after three years, everyone moves on like normal.
They we're sad, but once the shock wore off they are supportive of me dispite our different belief systems.
I am now divorced, due in part to my change in belief. My family has been overall supportive and I am happier than ever.