How to Get Crossette Xenoblade 2?

You get Crossette by accepting the “A Firecracker of a Gal” key item from the DLC Blade Distribution 2 section of the Expansion Pass, then talking to Hurryscurry at the Argentum's Bower Lounge. There's no quest to complete: you simply get the Ebullium Core Crystal from him, that is guaranteed to summon her.

Which driver is best for crossette?

Either Nia or Zeke are solid options. I lean toward Nia, simply because Zeke has other weapon types he's better with, while Bitball is Nia's best and (short of getting really lucky with a good common,) Nia has f*** all for good Fire Elemental blades.

How do you get Corvin in Xenoblade Chronicles 2?

Corvin is obtained by bonding a driver with the Divine Core Crystal, which is recieved from Sorinosori at the Goldmouth Return Port, Goldmouth, Argentum after purchasing the expansion pass.