Competitive in-game team help/critique

So I'm going to be battling my friend irl. We both know all the mechanics of battling like IVs and natures and stuff, and we both have Pokemon trained in that respect. However, I haven't been in touch with the metagame for a couple of years, so I'm afraid my movesets may be a bit outdated.

I know for a fact that my friend has DDtar, Metagross, Scizor, Aerodactyl, Heracross, Dragonite Jolteon and Gardevoir among his choices. I suspect he's probably running a sandstorm team. Now here is my team, as it looks right now:

Jolteon @ Leftovers
Timid
6/252/252
Thunderbolt
Quick Attack
Substitute
Baton Pass

This was my staple lead back in 3rd gen, but I'm not sure how well it works now. I used to run it with a Salac Berry but Sandstorm puts a damper on that.

Bronzong @ Leftovers
Relaxed
(Forgot what EVs I used, but probably 252 HP and some in Def.)
Stealth Rock
Gyro Ball
Light Screen
Rest

This will be my main counter to Metagross, TTar, Scizor, and Aerodactyl (and to an extent Heracross). I'm not sure Light Screen fits on this moveset, I'm thinking of replacing it with EQ so it can hurt Metagross and Scizor.

Blissey @ Leftovers
Bold
252 HP / some in Def / some in SpA
Toxic
Ice Beam
Softboiled
Aromatherapy

I'm actually debating on whether or not to include her. Most of my friend's sweepers are physical, so not sure how well she'd help. I may replace Toxic with something due to the abundance of steel-types, and probably replace IB with Fire Blast.

Gengar @ Black Sludge
Modest
6/252/252 I reckon
Substitute
Hypnosis
Shadow Ball
Focus Blast

My special sweeper. The plan is to send it out on something that's not TTar, Scizor or Metagross, sub, hypno, then do as much damage as possible.

Gyarados @ Life Orb/Leftovers
Adamant
6/252/252
Dragon Dance
Waterfall
Earthquake
Ice Fang

Late sweeper, hopefully after I've taken out his Jolteon already. Need help deciding between Orb and Lefties.

Now, I need some help deciding a 6th party member. Choices for me are:
Metagross - Right now it runs an Agiligross set, but I can modify it for lead or CB.
Azelf - Nasty Plot variant (can change to Specs)
Porygon Z - also Nasty Plot
Ninjask - standard BPer
Starmie - Choice sweeper
Heracross - Scarf variant
Slaking - CBer

I also have a nice timid Heatran that I can EV train in a day or two. (We're playing with a level 50 cap, so no need to level it up)

Anyway, C&C are appreciated. Thanks in advance.

Tyranitar, Metagross, Scizor, Dragonite, Heracross are all potential problems for most of these Pokemon. Any way you can score an Infernape? It counters all except Dragonite unless you can get a 70 power HP Ice then you can hit him hard too.

Unless I use my Lonely nature, 0 Speed IV starter Infernape, no, he's not viable.

I'm thinking of running Heatran over Jolty, and adding in either Hera or Meta for more physical support.

Well Lonely increases Attack and lowers Defense, which Infernape doesn't care about since his is low. Most people actually run Hasty which is -Def as well anyway. You can mitigate the 0 speed IV by investing extra EVs and running Scarf Ape which will counter Tyranitar after a Dragon Dance. He will also counter Scarf Heracross and Agiligross (Overheat can KO it), and Infernape can deal with Scizor if he can switch in healthy enough to take a Bullet Punch. Overheat will also do a number on Gardevoir and Scarf Ape Close Combat should deal with Jolteon if the Jolteon isn't scarf.

Lead Heatran over Jolteon and Metagross over Blissey should do you right. Blissey isn't going to stop most of these Pokemon. I say Life Orb for Gyarados since he's going to be a late sweeper and I find that the extra damage is very much welcome.

Substitute on Gengar is decent enough to scout switches but Hypnosis is so terrible at 60% accuracy. Even 70% in D/P is bad and can really alter the match adversely if it misses. I'm thinking Destiny Bond as a last ditch effort to take down a slower Pokemon with you?

Bronzong (and your team) would probably benefit better from Reflect and you may want to consider Light Clay for the extra 3 turns of it but that will cost Bronzong a little bit of staying power.

Run Infernape the lonely one, CB it and focus on using stuff like Flare Blitz/Close Combat where his defense isn't your worries and he has an entirely weak team to it 'sides Dragonites. Your other worry I'd say if you know he has DDtar, you don't have a solid counter for it without a Bullet Puncher etc.

Yeah, that's why I suggested Scarf. It counters +1 DDTar.

I'm not a fan of using Choice Pokemon as solo counters to a lot of things. You might want to use Life Orb instead so that Infernape isn't constantly switching out.

You might want to run Scizor for the DDTar, as DDTar often doesn't have the space to run Fire Blast and dies to two Bullet Punches or one Superpower.

While I usually don't like running a fire move on Blissey, Flamethrower or Fire Blast might actually be necessary because otherwise even Infernape isn't really an answer to Scizor (if the Ape is running LO). At least Blissey can withstand one hit (not sure about Superpower though. You might want to revenge kill then surprise with Fire Blast if you can). If you run Heatran like zeroality suggests then this is pretty much void.

If he runs LO Infernape, he won't outspeed a 1+ DD Tar so it's kinda moot of even having an Infernape as a counter to the whole team. Although if you know their whole team (Types, techniques etc) then do run Fire Blast on Blissey, a nice hit on Meta/Scizor will help when they switch in expecting to pull off something. Although the first hit may give it away so maybe try thunder wave over toxic since it's kinda moot against a Sandstorm team really and you do need speed support. Plus I doubt he has a heal bell dragonite so t-waving his whole team may be hugely in your favour. You won't require Infernape per se if you do run t-wave blissey. Electivire is also a nice choice to have around imo if he has a jolteon but I don't think that's an option ja?

I just beat him using a team of Jolteon, Bronzong, Metagross, Heatran, Gengar, and Gyarados. He started with Scizor, U-Turned to Metagross, I BP to Bronzong and set up SR and Reflect (w/ Light Clay). Then I just swapped between my Zong and Scarf Heatran and pretty much raped his whole team. Didn't even have to bring out Meta or Gyara.

Thanks for all the help guys. Even though I won, I'll still probably modify my team as suggested, just in case he wants to challenge me again.