Your team is quite weak to dark types and very slow. Ferrothorn doesn't fit anywhere on this team. You already have 2 steel types and you already have an entry hazard setter.
Ferrothorn -> Heracross
Heracross helps solve your dark type weakness, quite fast and a powerful sweeper with boosting moves.
Heracross @ Flame Orb
Ability: Guts
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Close Combat
- Megahorn
- Swords Dance
- Facade
Close combat & Megahorn as STAB moves. Swords dance to set up and facade to be boosted by guts and it's flame orb.
Slowbro -> Tapu Fini
Tapu Fini @ Leftovers
Ability: Misty Surge
EVs: 252 HP / 48 SpD / 208 Spe
Calm Nature
- Calm Mind
- Scald
- Moonblast
- Taunt
Adds a pretty quick specially defensive sweeper to your arsenal. Calm mind to set up, Scald and Moonblast as STAB special moves. Taunt to stall a little bit.