Before the Train and After Reaction

I'm rather lost with this piece. It sounds like the 4 individuals, Jeremy, Allison, Paul, and Marty are young children when Jeremy's hand comes off touching the oncoming train. But the way they communicate has me thinking these are adults. The strange discrepancy that caught my attention was the relationship between Allison and Paul. To me I think Allison is with Jeremy but she is kissing Paul by the middle of the story. I thought maybe these three or four individuals were in a band together and have a polygamous relationship. I feel Allison may be struggling with Jeremy's loss and she goes to Paul for strength, but its not clear to me. Allison is laying on the ground at one point feeling defeated or lost and Jeremy joins her. This to me was just her moping over her unhappiness.

Later on Allison and Paul are fighting with each other naked and move their argument into the kitchen where Allison tells Paul Jeremy has no hand. An obvious observation on Allison's part but I think was Allison realization of how serious Jeremy's situation is with missing a hand. Then bizarrely enough Paul puts his hand on a wooden chopping board of sorts as if he wants his gone. Like it'll somehow fix the problem. They consider it apparently. Paul tells Allison to be careful because the knife is sharp and it ends right there. This moment has to have some symbolic meaning to it aside from a potential literal one. Why does Paul offer to his hand cut off? How would it help, if at all?