I don't know your particular family situation so I don't have any personalized advice to give, but I would start with making sure you have at least some sort of closure with your family before departing. In your last days you could help them out a lot or just hang out with them. Have them understand that when you go, it's not because you don't love them, it's that this world wouldn't love you. I'm definitely writing a note if or when I go.
In the end I'm planning to make sure that none of them have to see what happened to me; and if that gives you peace of mind I'd suggest doing the same too.
If you have supportive parents (attempted to help you through this) I would thank them especially. A lot of people here hate their parents for valid reasons, I suspect that you probably don't if you are thinking about what will happen to them after you go.
Good luck, hopefully you'll have the peace you're looking for soon.