Tough choice. In the end I would chose the twelve year old girl. Though children would lose their father, they'd be able to recover, and potentially grow stronger. The recovering alcoholic, though she would lose her chance at getting better, at least she was given time to live. The girl is young, still has so much to experience, is still learning the way of life. The other two have had some time, and though it would be better to save them all, the one that has the chance to bring the most hope to the galaxy should survive.
If you had the oppurtunity to go back in time to a mistake you made, would you fix it? Or would you live with it, no matter who devastating, knowing it helped shape you?