Note: You should probably check Smogon for better ideas but this is my first reaction to the Pokes
I'm not going to mess with natures and all that but I'll mess with the items and maybe movesets if I have to.
Feraligatr ♂
Level 40
Nature: Jolly
Ability: Torrent
Item: Leftovers
Moves:
Crunch
Ice Fang
Hydro Pump
Surf
The reason I swtich Hydro Cannon is because if it hits you have to recharge, Hydro Pump is a little weaker, but more reliable and not forcing you into a stall. Generally as a rule of OU competitve battling, the Plates and elemental items are not as useful.
Gyarados ♀
Level 41
Nature: Naughty
Ability: Intimidate
Item: Dragon Fang
Moves:
Hydro Pump
Dragon Rage
Waterfall
Dark Pulse
Gyarados is a physical destroyer by nature (pun intended) so using special attacks with him isn't a good idea. He has a great move pool of physical attacks. Item wise, Life Orb or Leftovers.
Entei
Level 46
Nature: Bashful
Ability: Pressure
Item: Amulet Coin
Moves:
Fire Blast
Fire Spin
Stomp
Flamethrower
Amulet Coin isn't helping in a non-in game battle. Flamethrower is great, Will-o-wisp is a great compliment to it, because when inflicted with Burn, a pokes Physical Attack is reduced by 50% (unless it has Guts). Fire Spin doesn't really do anything other than residual damage with Sandstorm/Hail/or Burn would do anyway.
Raikou
Level 48
Nature: Lonely
Ability: Pressure
Item: Soothe Bell
Moves:
Thunder
Charge Beam
Spark
Shock Wave
Like Amulet Coin, Soothe Bell isn't good in a battle. The biggest problem this Rakiou has is that it's stalled by Ground pokes like my Swampert because Electric attack have no effect. Hidden Power of Ice/Grass/Fighting are really good with it. It can also learn Shadow Ball.
Ho-Oh
Level 50
Nature: Mild
Ability: Pressure
Item: Quick Claw
Moves:
Earthquake
Fly
Fire Blast
Sacred Fire
Fly isn't as good as it is in game, sure it makes a move miss one time...or lets them set up a free Calm Mind/Swords Dance/Dragon Dance/Curse/ etc. Brave Bird does a number as well as Scared Fire as STAB moves, Roost to Heal. The big threat to the Ho-Oh is Stealth Rock, every time it switches it'll lose 50% of it's health. If you use entry hazards, whirlwind is a great choice, if not Earthquake is fine for non-flying pokes
Latias ♀
Level 35
Nature: Naughty
Ability: Levitate
Item: Exp. Share
Moves:
DragonBreath
Psychic
Refresh
Mist Ball
Dragon Pulse does more damage then Dragon Breath, Psychic is okay, Recover/Wish is more effective than Refresh, Mist Ball is okay, but you could also use Thunderbolt for type coverage.