Skylanders: Spyro's Adventure/WMG

The Skylanders' names (save for Spyro and Cynder) are nicknames.

 * It makes sense, given the punny nature of the names, and how some Skylanders (such as Ignitor and Drobot) haven't been that way all their lives. It could also refer to occupation, such as Gill Grunt being a grunt of the gillmen. Given that their battle cries have an in-canon explanation as being Skylander tradition, it wouldn't be surprising if their names were chosen upon entry to the Skylanders too.

Whirlwind is Rarity and Spike's daughter.

 * That makes some kind of sense.

The Giants in the sequel are the Elder Elementals mentioned in the first game
The first games mention Elder Elementals, powerful ancient Skylanders. The Giants so far revealed all have elemental appearences and are more powerful than the normal characters, so it would make sense.