What level do they evolve at?
To evolve Seadra you must trade it while it is holding a dragon scale. To get Growlithe to evolve, use a fire stone on it. Neither of them level up through evolving.
Just see this
Seadra Evolves Into Kingra if You Trade Him Holding The Kings Rock. Growlithe Evolves into Arcanine, if you use a fire stone.