This question was not so cut and dry for me.... seeing how I would have to physically make a choice in all but one of my options.
I don't think I could just not do anything and let the train destroy the love of my life, and I don't think I would send the train over the cliff.
But is the act of pushing the fat man any different than changing the coarse of the train? Well he does have free will... meaning he just happens to be next to me, he is not forced to be there, where the people on the track cannot move.
....It is still a tuff decision, but I would push the fatman in front of the train.
In this decision there would be only one life lost, granted it was from my direct action. And who knows... maybe the fat man parked the minivan on the tracks. I say this because the question said nothing of a driver being in the minivan.