Question: Why does Melvin, who looks about 15, live out there alone, in a shack, with no adult supervision??
Answer: Melvin is Nestor's stepson.
Question: Wouldn't Burt and his wife get in trouble for having all the weapons in their house? Even in later movies, there is no sign they got in trouble and Burt continued to have all these big weapons on hand.
Answer: No, there's nothing illegal about any of the weapons they owned. Some of them may have required a Class 3 firearms license, but even this is not difficult (just expensive) for a law-abiding citizen to obtain.
Question: Before Burt and Heather are attacked in their basement by the graboid, she puts some bullets and dirt in a machine and turns it on. The machine makes noise and attracts the graboids. What is that machine doing to the bullets and dirt?
Answer: The machine is a vibrating case cleaner, which is used to polish the brass casings of pistol and rifle ammo. The "dirt" is actually an abrasive polishing compound.
Question: I know the movie is called Tremors, but are the monsters called "tremors" or "graboids" or "snakeoids" or something else?
Answer: They officially name the creatures "graboids", as that's also what they call them in later films. Tremors is just a clever movie name, and "snakeoids" was just one of the potential names the chinese guy and the kid were thinking of naming them.