Hiya, Dragonbones is a free piece of software, you do not need to pay for the animation software. The pack clearly states it is a free pack of Generic enemies that are dragon bones files, if you read my terms and conditions (namely point 5 and 6) you'll see this referenced. If you are using Rpg Maker MV, the Dragon bones Plugin is free last i checked.
The gifs in the pack are 'preview' folders they are not meant to be used in games they are there so you can see what each 'motion' of the Dragon Bones battler looks like and does and what they are called. This is why they are inconsistent in size, they just exist to showcase the motion.