Trailer axles for tandem single wheel start at 3,500 lbs. then it’s typically 5,200; 7,000; 8,000.
Two 3.5k is a 7k trailer. Usually, only one axle will have brakes, on this size. Typically has a 2” ball.
Two 5k axles is a 10k trailer. At this point, you’re likely to see brakes on each axle and move to a 2 5/16” ball.
Two 7k axles is a 14k trailer. Almost always has brakes on both axles, 2 5/16” ball.
The 8k axles are fairly rare. They often have bigger wheels to accommodate the heavier load rated tires.
The GVWR, say 14,000 lbs, includes the weight of the trailer and the load. The bigger and heavier built the trailer, the less you can haul. Some GVWR’s will allow for tongue weight (the weight the truck holds).