For Bronzong, you might want to make it Relaxed to pump up Gyro Ball's power (it gets stronger the slower the user is than the opponent) and improving Bronzong's physical bulk.
Kingdra is an excellent Special or Physical Rain Dancer; it should go over Chimecho, since it's not that good above NU:
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb/Lum Berry
Ability: Swift Swim
While Ludicolo is usually seen with offensive sets in rain, a defensive set can be used viably. Change the nature to Calm or Bold and make the EV spread 252 HP/252 Def/4 SDef (Bold) or 252 HP/4 Def/252 SDef (Calm).
Not all your Pokemon have to have Rain Dance. Slowbro can function just fine even without Rain Dance in its set:
EVs: 248 HP/244 Def/16 SAtk
Having Omastar on the team would add to the team's weaknesses. Xatu is a better Rain Dance setter because of its Magic Bounce ability:
EVs: 252 HP/4 Def/252 SDef
Ability: Magic Bounce