Training my level 50-60 pokemon on pokemon pearl

Question

i need some help finding some good places to level up my pokemon. here is a list of my pokemon i need to level up.

fearow lvl 51

banette lvl 54

sneasel lvl 55

roselia lvl 51

camerupt lvl 55

please give me some answers.

Answer 1

use vs seeker and keep fighting the last sailor just before sunnyshore. he gives around 2000xp per defeat

Answer 2

you can train at the elite four if you havent beaten them i will give my dialga level 99 to you code is dean