I think that the best would be:
4 Piplup DP
2 Prinplup DP
3 Empoleon MD
1 Empoleon Lv.X
You could play 1 empoleon DP if you think you need that extra 10 damage from his first attack, but i personally prefere the MD empo.
Empo lv.X it a really nice sniper. He could kill your opponent's claydol and earn you your last prize.
For omastar i'd go like this:
2 Helix(if you could afford to play 3 it would be better, but space is a bit tight sometimes)
2 Omanayte
2 Omastar MD
1 Omastar PK
Playing a fossic excavator could help in getting that Helix fossil, but it's not necessary)
and playing 3 SSU could be really helpful.
And then for phione:
3 Phione
3 Call
3 Roseanne's
i don't like playing 4 call since you won't need it after the first few turns.
That is a basic idea of how to play empoleon.