Cross the bridge over the water into the first patch of grass, then follow it North to the first trainer on the route.

Battle: PKMN Breeder April (864 Poke)
Opponent: Minccino Lv 27, Deerling Lv 27

Continue through the forest back across the river heading East, where you'll find a trainer with a large umbrella.

Battle: Parasol Lady Nicole (896 Poke)
Opponent: Castform Lv 28

Nicole's Castform is sadly out of luck out here- there's rarely any weather going on, so it doesn't get to change into a form.  This leaves its Water Gun weak and it without any particular characteristic or advantage.

North of her you can find a little girl looking for a fight.

Battle: School Kid Mara (540 Poke)
Opponent: Deerling Lv 27, Shelmet Lv 27

Mara's Shelmet is a bit annoying for physical attackers, as it mostly just sits around Curse-ing and Yawn-ing.  Thankfully, it doesn't really -attack-, so it's just a time-sink.

Check the ground around Mara- there's an Elixir in an item ball to the right of her- and behind her is a Foongus disguised as an item ball!  Foongus are annoying, but not too threatening if you have an antidote on hand, so take care of that if you feel like- or catch it.  Foongus and its evolution Amoongus are pretty standard Grass/Poison pokemon with debilitating status effects to inflict and decent sturdiness.