death in family, how to show support?

Let me start by saying, this person wasn't technically "family" but was with my cousin for 5-6 years! As I'm scrolling through Facebook I see A. Post about losing a sister, that sister was my cousins girlfriend! Apparently my sister and J. Went out on some 4 wheelers last night, while riding they was drinking! (Beer!) Stupid I know... I guess J. Was driving when she kicked it into a higher gear and lost control, the person who was on the back with her got thrown a few feet and has a broken wrist, as for J. She had massive amounts of internal and external injuries. (Brain contusions, bleeding in the intestines and colon, a messed up face, ect.) My sister S. And her boyfriend grabbed up J. And rushed her to the ER, when she got there she died, they got her back and stable to be flown out ASAP to a nearby, much larger hospital! They eventually took J. To surgery but later hemorrhage dot her death. J. Leaves behind some little girls as well as plenty of people who cared for her! HERE is where I'm needing help! How can I be more supportive? I've just got so much shit to say that might come off as rude and unwanted, I'd rather not ruin any relationships by what I want to say! Like why in the hell didn't they call 911 instead of movin J.? Or why in the fuck my sister left her daughter after she had surgery to remove tumors? Or why in the fuck was they drinking knowing damn well my sister isn't even 21? Or why they even went 4 wheeling in the damn dark, while drinking! Seriously it's super hard to be supportive when each and every one of them was so stupid in this situation! According to my sister she was supposed to be on that same four wheeler but her boyfriend said no it wasn't safe!?!? Then why in the world would you let someone else go? I'm seriously so aggravated that they could be so stupid to do this! One of J. Daughters doesn't have a father (my cousin is a woman who is a lesbian who stepped up to be daddy!), I mean she technically does but he wants nothing to do with her. These girls needed a mother in their lives and now because of their stupid ass mistakes they have no mother! Again HOW CAN I BE MORE SUPPORTIVE WHEN I JUST WANT TO SHAKE THE LIVING HELL OUT OF MY 19 year old sister?!?!?