Your team is very solidly levelled, except for that Fearow, which likely won't be too much help. You could use it as fodder while you heal other team members, but that's about it.
First up: Golisopod. It'll start with First Impression, so don't lead with Decidueye or Bruxish. Whiscash is so overlevelled that it could probably tank a First Impression, then take out the Golisopod with ease. Another option is your Alolan Graveler. Get an Eviolite from Konikoni City to boost its defenses, then wipe the floor with Golispod with a super effective Electric move. But be warned -- Golisopod packs Razor Shell.
The Masquerain shouldn't be a threat at all, blast it away with Alolan Graveler's Rock moves. If that somehow fails, Torkoal could likely do the job nicely.
Pinsir can also be dealt with easily. Use Alolan Graveler or Torkoal again to take it out, but be warned of its Storm Throw and Stone Edge.
For Vikavolt, take the same strategy as the others. Use Torkoal and Alolan Graveler with their super effective moves, with Whiscash as backup.
In conclusion, you should grab the Eviolite from Konikoni City, put it on Alolan Graveler, and use it and Torkoal to take down Guzma. Whiscash can be backup, Fearow as healing fodder, and Decidueye and Bruxish should be kept out of the battle.
Hope I helped!