First Trainer (B1 level)
Both pokemons use highly damaging moves: Rock Blast and DynamicPunch. Lowering their accuracy (eg. Smokescreen, Mud-Slap) is a good way. Ghost-type pokemons can be used to negate the DynamicPunch damage.
Second Trainer (Ground level)
Pokemon with high defense is suggested. Starmie using Bubblebeam and Confuse Ray can prevent Steelix using the Stealth Rock while tackling the Ground-type weakness. Alternatively, Stealth Rock can be removed by Rapid Spin. Gengar can be used to neglect the Double-Edge damage while using Hypnosis to block the use of Stealth Rock. Ghost moves have *1 multiplier on Steel-type pokemons although the pokemons cannot be poisoned.
Third Trainer (Ground level)
Since Torkoal has White Smoke ability, any debuff moves are ineffective. Its Flamethrower is a strong fire move. High defense water-ground or rock-ground type pokemons can be used to minimise fire move damage.
Luvdisc can be easily dealt with grass or electric type pokemons.