DR Swishy the loss of your young friends, and I consider Jean young, is so very sad. To die so needlessly in such a manner just isn’t right.
When I was your age I lost friends & family to drugs. In my teens I almost lost my mother a number of times to drugs, it was very painful. I don’t think there is any special advice you need to give to your friends, just let them know you are there to listen anytime they want. Often people don’t want to listen so the grieving stop talking.