Why does Andrew continue to fight Matt at the end of the film? Stop and consider what Andrew repeats throughout the fight, that he is an Apex Predator. What do most Apex Predators do when they are challenged by another one of their kind? They fight in order to establish dominance. Andrew sees Matt's stubborn refusal to get out of his way as challenging him for the role of the Alpha male.
It's also possible that after all he's gone through, his father's relentless abuse, Steve's death that he's indirectly responsible for, his mother's death despite his best efforts, and the blinding pain he's no doubt in despite the painkillers, Andrew might WANT someone to kill him.
The three boys show elements of Personality Powers. Andrew, the loner who wants to be stronger and actively pushes people away, develops his telekinesis control faster than the others and is also best at erecting defensive barriers around himself. Steve, the industrious go-getter, is the first to try moving really big objects and the first to figure out how to fly. Matt wants to be unique, but he's overly cautious and is thus the slowest to develop of the three, but ultimately becomes the most powerful by the end when he takes matters into his own hands.
If you pay attention there seems to be some establishment of Magic A Is Magic A. The obvious take on this is how its shown that their powers are indeed like a muscle and get easier to use the more they use them. But the next bit comes when you pay attention to the times that Andrew is describing how to use their powers. In the Lego scene he tells Matt to, paraphrased “imagine like your squeezing it with your fingers", and when he explains how he gets his camera to float, he says the trick is thinking of it like he‘s holding it in his hands. And as disturbing as his explanation of tooth pulling is, it’s insightful that he describes “lassoing” the teeth. All of it shows that the force in question is kind of like a solid object being projected from the guys mind’s.
The use of "Ziggy Stardust" for the scene where Andrew puts on his dad's costume and really starts giving in to his Dark Side; the lyrics basically sum up the entire story - three childhood friends who set out doing something they love, but the greatest of them (who's a Decoy Protagonist) is destroyed by going too far and it's up to his friend to put a stop to it.
Ziggy really sang, screwed up eyes and screwed down hairdo
Matthew was not made aware of his uncle's abusive behavior towards his cousin before having to kill Andrew. It is possible Andrew viewed Matt's rescue as support of his uncle's abuse. Such a gross betrayal on top of everything else Andrew had been through might turn anybody into an Omnicidal Maniac.