Even if modern slicers have gained a lot of advanced features, to my knowledge the gcode they output is still very simple. You can put all kind of fancy commands in the start and end gcode, but the actual printing part consists almost exclusively of commands that move the nozzle to a specific XYZ coordinate, and/or make the extruder motor move the filament either backwards or forwards.
Maybe ask your brother about what software he used it with? If the printer has an sdcard reader it might be easier to print off that than try to get it to communicate with a computer. I don't have any first hand experience with that old printers, but I would guess it uses some kind of serial over USB protocol similar to modern printers. If you're using Windows I think you might need to track down a driver for the printer's serial controller, but if you have Linux there's a chance it has the necessary drivers built in.