Help with my Pokemon Platinum team?

Okay, so I've been having some trouble with my Platinum game and my team SUCKS.

How can I help my team and level them up?

Here they are:

Luxray - 50 - Intimidate

Moves: Thunder Fang, Charge, Crunch, Strength

Umbreon - 49 - Synchronize

Moves: Faint Attack, Bite, Shadow Ball, Assurance

Empoleon - 51 - Torrent

Moves: Surf, Brine, Peck, Waterfall

Drifblim - 41 (yeah ... I kinda wasn't paying attention to her) - Aftermath

Moves: Payback, Ominous Wind, Fly, Baton Pass

Giratina - 47 - Pressure

Moves: Rock Climb, Rock Smash, Dragon Claw, Shadow Force

... yeah I only have 5. I have these pokemon in my PC:

Froslass, Vulpix, Gabite (If I'm gonna add gabite, i'll get a new one in VR), Swablu, Magmar

And at the moment I am doing Victory Road, so that's why I have so many HM's on my pokemon. After VR I'm getting them removed and putting TM's on them.

1 - What should my last pokemon be?

2 - Should I change anyone on my team?

3 - Other than Items and luck, how will I do after leveling them up (to probably 55 - 60)?