Are there more than just twelve bonus characters in super smash brothers brawl

No.
You can unlock Ridley And Tabuu, Here's how:

Ridley:Defeat Tabuu (Adv. not boss battles) 3 consecutive times with samus as your first pick without dying

Tabuu:Defeat The Subspace Emissary (not just tabuu, everything else) 30 times with at least hard difficulty, play 1,000,000 Brawls, Use 10,000 final smashes.