Alright bro's here's your gym leaders.
Brock
Pokemon
Geodude level 13
Onix level 13
Lileep level 14
Omanyte level 14
Carkol level 15

Misty
Pokemon
Palpitoad level 21
Huntail level 22
Gorebyss level 22
Araquanid level 23
Starmie level 24

Lt Surge
pokemon
Emolga level 27
Rotom-M level 28
Zebstrika level 28
Raichu level 29
Manectric level 28
Arctozolt level 30

Erika
pokemon
Ludicolo level 36
Leafeon level 37
Gourgeist-S level 37
Vileplume level 39
Victreebel level 38
Ferrothorn level 38

Koga
Pokemon
Dragalge level 45
Scolipede level 46
Crobat level 48
Roserade level 46
Tentacruel level 47
Muk-A level 47

Sabrina
Pokemon
Metagross level 52
Alakazam level 55
Hatterene level 53
Sigilyph level 54
Medicham level 54
Jynx level 53

Blaine
Pokemon
Talonflame level 61
Darmanitan Galar level 62
Marowak-A level 62
Rotom-H level 63
Volcarona level 63
Arcanine level 64

Giovanni
Pokemon
Gliscor level 68
Flygon level 69
Golurk level 69
Nidoking level 70
Mamoswine level 70
Rhyperior level 71