Lorelei:

RBY:
Dewgong LV 54 (Aurora Beam, Bubble Beam, Rest, Take Down)
Cloyster LV 53 (Clamp, Ice Beam, Spike Cannon, Supersonic)
Slowbro LV 54 (Amnesia, Psychic, Surf, Withdraw)
Jynx LV 56 (Double Slap, Ice Bean, Lovely Kiss, Thrash)
Lapras LV 56 (Blizzard, Body Slam, Confuse Ray, Hydro Pump)

Use:
Use some strong Electric or Grass Pokémon, and you should do fine.

Bruno:

RBY:
Onix LV 53 (Dig, Rock Slide, Screech, Slam)
Hitmonchan LV 55 (Double Team, Fire Punch, Ice Punch, Thunder Punch)
Hitmonlee LV 55 (Double Kick, Double Team, Mega Kick, Hi Jump Kick)
Onix LV 56 (Earthquake, Rock Slide, Screech, Slam)
Machamp LV 58 (Karate Chop, Leer, Strength, Submission)

Use:
Attack these Pokemon with Water, Fighting, or Psychic moves/Pokémon.

Agatha:

RBY:
Gengar LV 56 (Confuse Ray, Lick, Mega Drain, Subistitute)
Golbat LV 56 (Leech Life, Supersonic, Toxic, Wing Attack)
Haunter LV 55 (Confuse Ray, Dream Eater, Hypnosis, Lick)
Arbok LV 58 (Acid, Glare, Screech, Wrap)
Gengar LV 60 (Confuse Ray, Dream Eater, Hypnosis, Psychic)

Use:
Whatever attacks you used in the Pokémon Tower, use them. I've used Fire, Electric, and Water attacks. And they seem to work.

Lance:

RBY:
Gyarados LV 58 (Dragon Rage, Hydro Pump, Hyper Beam, Leer,)
Dragonair LV 56 (Hyper Beam, Slam, Thunder Bolt, Thunder Wave)
Dragonair LV 56 (Bubble Beam, Hyper Beam, Ice Beam, Wrap)
Aerodactyl LV 60 (Fly, Hyper Beam, Swift, Wing Attack)
Dragonite LV 62 (Blizzard, Fire Blast, Hyper Beam, Thunder)

Use:
Ice Pokémon seem effective against these types. Or you can use another Dragon type. Any final-form Pokémon, that knows Hyper Beam, should work the best.