[quote=@Banana]
I'm going to assume that there are other Pokemon nerds here aside from Birb, and I'm going to post something off-topic.

I'm trying to get a good doubles team together on my copy of Sun, but I've hit a roadblock and desire to train up some more 'mons to use for a potential team.

Right now I have a solid 3 'mons for the future team, with those 'mons being Loan Shark (Garchomp), Shock Hawk (Tapu Koko), and Marvin (Celesteela).

I've hit a rut with my team and I don't know what to add onto it, so if anyone has any ideas, please feel free to pitch in. I'm considering Oranguru at the moment if it helps at all.
[/quote]

Depending on your play style, I've gotten pretty far with my Tsareena (Mainly cuz I'm a weirdo who finds plant girls attractive). Queenly Majesty to prevent priority moves, mostly Fake Out and Protect. Her other moves are Teeter dance for AoC Confusion, Trop Kick as her stab, and Protect if I know there are enemies I can't one-shot. I don't do doubles too often though, though when I do and start with Tsareena I either retrain Teeter Dance with High Jump Kick or, depending if the partner pokemon is not particularly item dependent, just give them a lum berry. 

A different, more grindy strategy that you could try but may be difficult for you to pull off in Sun is trying to find yourself a Alola Ninetails. I was able to pull that off on my sister's Pokemon Moon after an hour of hunting. After that just buy TM 70, Aurora Veil, from Heahea City and watch from turn one your Ninetails halves all incoming damage for five turns. Hardly anyone runs brickbreak these days. Granted, as someone who first started in Gen III, this is obviously a more weather focused team. I pair up my Ninetails with a Frolass with snow cloak to summon blizards and set up entry hazards. Beyond that I don't have much else on Ninetails that's very competitive. Blizzard, Dazzling Gleam, and Roar once the Frolass has set up the entry hazards.