STAB stands for "Same Type Attack Bonus", which in damage calcualtion makes a move that is the same type as it's user do 50% more damage than a similar powered move that isn't the same type as it's user. :P
Vikavolt, Arbok, and Hariyama aren't great in the Battle Tree, so you may be better off replacing them with Medicham, Nidoking, and Volcorona (if you want to replace them with similar Pokémon and you have access to them), but I'm sure there are a lot of Pokémon in Alola worth using. :P
You may want to work on your natures and abilities (and maybe items, but that can wait until you get some BP), as not all of them may be the best for your Pokémon. :P
Having 4 Z-stones on 1 battle tree team isn't necessary; you only need 2. You should also look into investing in 2 Mega Evolving Pokémon (Metagross, Salamence, Medicham, Gengar, ALakazam, and Lucario are Native to Alola and great for the Battle Tree). You can use the Tapus for the Battle Tree, so you may want to consider that as well. :P
Having a lot of moves of the same type is pointless when they don't do much for the Pokémon: You don't need Grass Pledge, Draining Kiss, Sludge Bomb, Reversal, Payback, and one of Dark Pulse or Night Shade. :P
You seem to run most Pokémon with a Physical and special attack. With a majority of Pokémon, this is a very bad idea, and running both Special and Physical moves on a Pokémon shouldn't be done unless you absolutely know what your are doing. I think the only Pokémon on your team currently who should do this is Zoroark- and if you do, it's only Physical move should be Sucker Punch. :P
What EV's do these Pokémon have, or what EV's to you plan to train them with? What IV's do they have? :P
