Magmortar - If you want a special attacker, i'd personally put Modest and attach a choice scarf to it. But if you want a mixed attacker, which works rather well, Mild or Rash is good too, with a life orb or expert belt for the extra kick. Life orb is recommended since you'll be a gym leader and be hit mostly by super effective moves (i'd know), so you need the most damage output u can get. For moves, you want coverage, especially against types like water, rock and ground. I'd put Fireblast/Flamethrower, Thunderbolt, Focus Blast and probably Hyper Beam (when ur gonna die) or SolarBeam (if you use Sunny Day). Having Sunny Day will also help your team heaps, it eliminates water weakness (halves water damage), and lets negates the Solarbeam charge up. EVs would simply be 252spatk and 252speed. Make sure your HP isn't divisible by 4, since stealth rock damage rounds down.
Infernape - I would put this as your lead, simply because it learns Fake Out. If you use Fake out on an oponent with focus sash, Fake out kills the focus sash, damage ur opponent, and they flinch. So you get a free turn. Also, you may be able to kill them before they can move, since infernape is rather strong. Furthermore, you might even kill there Stealth Rocker, without them able to put down SR, which your team really fears. For moves i'd put fireblast, close combat, fake out and maybe encore, incase they do get a chance to put stealth rock down, you can encore them into it so they are forced to switch, but you will need prediction for this, (if you know aren't going to KO them, encore them first so they are stuck and have to switch.). EVs i'd go with max special attack, enough speed to outrun what you want to, 339 speed outruns Adamant Dugtrio, the rest into Attack to increase Close Combat and Fake Outs damage. Item should be Focus Sash or Life Orb to increase your chances of getting the KO first. Naive Nature is preferable, although Hasty is alright too.
Rapidash - for rapidash, i'd go with the moves Hypnosis, Flare Blitz, Megahorn and Iron Tail. Hypnosis first to sleep something, and attack. Flare Blitz for STAB, Iron Tail to hit rock types effectively, and MegaHorn is your strongest attacks against water types. Nature should be Jolly to have the greatest possible speed. EVs can be 252atk, 252speed. Again, make sure HP isnt divisible by 4. As for Items, I like wide lens, simply because it raises accuracy for Hypnosis, Iron Tail and Megahorn. As a gym leader, its rather annoying to miss an attack and lose.
Blaziken - I dont know much about blaziken to be honest.. i thought it was just a weaker version of infernape
.. so you'll have to ask someone else...
Typhlosion - Not sure about this guy too.. but he does learn Solar Beam, so if you're using Sunny Day, make sure you use solar beam on it, also, use Overheat and a Choice Scarf or Specs on it. I recommend Scarf since you need a speedy revenge killer. I'd go with Modest Nature and max speed and special attack.
Charizard - Not sure as well... just go with what Death said
Overall nice team i guess, but i'd use Heatran since its really strong, a scarfed one is really good. Also, try Arcanine since Extreme Speed is good for revenge kills because of priority. Not much more i can say except good luck with the team. Also, Ninetales is good since it can Hypnosis, then it gets a free nasty plot, and has Energy Ball (good against ground, rock and water), and it's speed isnt too bad either.