With the first scenario:
First of all why are all these people playing the damn train track or just standing their?

• we must assume then that these people either work for the train line, or are just stupid. Perhaps there crossing the track... But still, you gotta know if you're on a train track the train is going to come.
• I will assume that they're not stupid and that they work with the train line, with this thought the solo person is obviously the foreman and the five people on the other side are the employees. In this case foreman bears responsibility for the employees (*Capt. must go down with the ship). So yes, we'd send the train down the track with the one person as they messed up with the timing of their work orders on the tracks.

The modification of the first one, and the solo person is my family member.

• We are assuming that a train moving at a speed fast enough for people not to get out of the way, I personally have enough time to recognize the person on the track and flip a switch. I'm going to have to assume they do not have that much foresight to realize that is my family member or best friend, again I will default the above statement and send the train down the track with the one person.
• If in some strange twist I realize that it is my best friend or family member... I would probably like with the f*** are they doing here, and in that moment disbelief the train would just run down whatever track it was supposed to be on. So I guess my action would be no action.

Let's look at the third preposition that the fat man would be pushed in front of a train.

• So let's just assume the crazy hypothetical that a fat man being pushed in front of a several ton steaming locomotive could stop it, and that through this gooey mess the train would slow down in time to save the five people... So those five people would need to be at least 100 yards away.
• First you would now be a murder if you push this person. This would then does have its own consequences, namely you would go to jail and maybe be executed. This would also result in costs, stress on your family and friends, if you have kids you'd be causing them years of mental anguish and they would have to visit you in prison, or witness you get executed.
• Also we are assuming that you can actually push this person who has tonnage that can stop a train.
• So I would say no, I would not push this person for the myriad of legal ramifications that come after it, and your personal mental anguish as you kill somebody and there's no guarantee that those people down the track would not have gotten out the way. and also you don't have guarantee that that person would stop the train I mean how would you know it? We are assuming that through some divine intervention I know pushing a fat person in front of the train would stop it? what if it didn't work and you just killed that fat person and the five people?

Fun thoughts. Thanks for get my brain moving on a Monday morning!
I'm going to hang out by some train tracks now and try to save people. :P