Kirsten gave you some very good answers. Guilt is a toughy! What right did your father have at your young little age to ask you such a thing, when he (through a choice not his) left! He had NO right to lay that burden on you!
You are God's special creation, he loves you, has plans for you and your gifts. Let the old guilt go, buy them all a lottery scratch off as your final parting gift, move out, and go on your own. You can still buy them scratch off's of course!!
They all sound like adults and they need to be responsible for themselves! Maybe set your siblings a good example and show them how to move out and go on their own....
My heart goes out to you. I know you are trying to do the right thing, and the right thing may have a definition different than you know.