My opinion is to change your medicham’s nature to +speed, outspending the enemy is often more important than extra firepower in reborn. And maybe salamence, but it has ddance so I’m not sure.
As for movesets,
Medicham - HJK over drain punch for me, the former gets a lot more of OHKOs, and mega medicham is somewhat frail and doesn’t need that extra recovery most of the time.
Salamence - you can experiment roost over fire fang for longevity, since you have ice type coverage on other mons. This works better with intimidate, since it lets mence have more setup opportunities. But salamence is very flexible so you can change the sets according to the enemy.
Tyranitar - Are rocks compatible with assault vest? xD EV wise, I’d always spec 252hp first for a bulky set, if you’re running vest then additional 252 def might be good. Also, sandstorm already gives rock mons 1.5x spdef boost so you can try leftovers too. Then you can use rest + toxic, or some other cheese sets if you like
As for the other mons I’m not too sure (rarely use them before), but I can give you some other generally good suggestions:
1. Rotom-wash - Will-o-wisp / Volt Switch / Hydro Pump / Snatch (flexible) 252 Speed, 252 HP or SpA, Leftovers
A really good support mon, will-o-wisp to cripple physical attackers, volt switch for pivoting, screens or hydro pump depending on the situation, it’s a really flexible mon. Plus, levitate allows you to predict ground type attacks and give it free switch ins. I suggest it to replace jolteon, since jolteon is a little one-dimensional.
2. Aegislash - King’s Shield / Swords Dance / Shadow Sneak / Iron Head, 252 HP, 252 SpDef, Leftovers
A bulky setup sweeper set, really a good mon against the AI. Because of it’s two forms, setting up is really easy, and it can decimate whole teams after setting up successfully. Might need a little time to understand it’s mechanics, but once you do, it can solo even (some) of the toughest fights.
3. Other than that, Volcarona and nature power Mega Sceptile are good options for special attackers as well.
Ok that’s a ton, but it’s what I can come up with, only personal experience though :3 In reborn, getting thrashed is really a common thing, especially for the first time, so it’s good to have some mons in rotation as well! Have fun with the game~