My take on these three is as follows:
Scorbunny - I'm 99.99% certain this is their primary mascot Pokémon for the Soccer side-theme, as the 'pads' are located on the bottom of its feet and on its forehead - it likely uses them like abrasive matchpads to generate fireballs for the feet, or ignite solid objects with the forehead. Both locations are heavily used in the sport of soccer, so this clearly is intentional placing on Game Freaks part. Its name can also be taken as 'score-bunny' as well. Evolution-wise, I'd expect the small pads to turn into sports tape-style wraps and a heavy focus on a 'Captain Tsubasa-esque' Soccer Striker theme. For eventual typing, while Fire/Fighting is always on the table, I'm getting the feeling that we may get our first Mono-Fire-type Stage 2 starter since way back in Generation 2 - we know how poorly-received the Fire/Fighting starters get with many older players, and a mono-Fire final evolution would ease the amount of punishment super-effective attacks can do to it. Also, there's a good chance Scorbunny will have a rival Pokémon of the Electric-type (and potentially Electric/Fighting) with a possible 'Inazuma Eleven' inspiration for an opposing team...
Grookey - As mentioned by others, the footprints left by Scorbunny regrew in Grookey's wake, either being relevant to its abilities or just to symbolize its Grass-type. I do think the stick it uses has relevance though - the positioning of it in its leafy hair makes Grookey's head resemble some sort of branch-hanging fruit, the first coming into my mind being the Pomegranate. I have no idea if pomegranates have anything to do with European folklore or such, so I won't speculate on it further. For its evolutions, I don't have much hopes for it - it could either become a Baseball themed slugger, focusing on the stick it uses, or just drop its tail and become a hulking gorilla (respawning all the Harambé memes again). Any typing could be chosen here, it just seems 'meh' to me.
Sobble - This is the Pokémon I'm most interested in as far as physiology is concerned - it's an amphibious lizard/chameleon-like thing with stick-like water strider legs and feet - something only insectoid Pokémon usually have. Its invisibility is just it using Acid Armor, which is a nice defensive change for this generation. It's also the Pokémon with the most potential in regards to its Evolutions - it could do anything from growing more feathery fins, transforming into a quadripedal Axolotl Pokémon, to going full Chimera with an aquatic Nue-like hybridized form. I honestly have no idea how Sobble is going to evolve, or what types it will become.
I'll still likely be choosing Scorbunny as my starter unless Sobble gets a great set of evolutions, but its design just screams to be a FIFATM promotional gimmick - and that's my take on the starters of Pokémon Sword and shilled, I mean Shield.
