Well considering your Conkeldurr holds a +SpD nature, you could try training in Attack (to the max), and splitting the rest between HP and Special Defense. This would work with a Bulk Up set ingame btw. Alternatively, train in HP and Attack instead. Just don't train in speed, it's speed is horrible anyway, and yeah you could go trick room.
Scizor is another physical attacker, so EV train in a similar way to Conkeldurr. Alternatively, you can dump all the evs onto Attack and Speed. If you're going trick room with him, train in a similar fashion to Conkeldurr still, and don't bother in defence since defence hindering natures sak :c
Chandelure is a special attacker, and since you already have a speed boosting nature, train it fully in Special Attack and Speed. No point running him in Trick Room, his already got a speed inducing nature might as well abuse it.
Gyarados can't have Swift Swim you hacker ;~; jks, you probably mistyped or got it off from a hacker. Errm EV train in Attack and Speed. Base 81 Speed really isn't slow enough for Trick Room. JS :P
With Haxorus you're supposed to EV train in Attack and Speed. But you're using a speed hindering nature ;~;. You can still EV train in those areas, and if you get Dragon Dance on it's moveset, that'll help with speed problems. Haxorus's base 97 speed means it sucks in Trick Room, even with a speed hindering nature.
And since you wanted to know which is better in Trick Room (I think?) between Conkeldurr and Scisor, I back Conkeldurr.
This is because Conkeldurr has overall better bulk, allowing it to switch in with less damage taken after Trick Room has been set, and also it's lower speed (base 45 compared to Scizor's base 65), it'll technically 'outspeed' more :P.