I bet the conference will be beneficial. Your grandchildren know you are coming back. You will be there for them in the coming months/years. I like the Serenity prayer for situations such as this because all you can do what is in your hands to do something about, nothing more. Best wishes.
Ronni, I got the chills reading about your loss. I have just gone through an attempted suicide with my mom. She tried to kill herself the day after Christmas. She was sent to acute care after leaving the hospital for 4 weeks. With all the counseling she received she has no idea what she did to the family. I am her caregiver and still having a hard time dealing with it. It doesn't matter what age you are it is devastating. I hope the girls get counseling, they really will need it. I'm sure they have asked themselves if it was their fault or if they could of done more. My prayers are with you and your family.
You can take your guilt outside and bury it so deep that it never resurfaces. You are doing all you can do and more, and you're allowed to feel angry. Going to the conference sounds just right. You get a break and some input and you'll be better equipped to handle your granddaughters' grief. They have a wonderful grandmother. We should all be so lucky.