Starmie and Keldeo will cause a lot of troubles to your team as you only have one extremely frail Water resist, which is Breloom, who takes a ridiculous amount of damage from even resisted Special Attacks, so it's a miracle if it's able to take an Ice Beam or a boosted Hydro Pump. You give both of them good opportunities to switch in with Heatran. Genesect might be able to check Starmie but keep in mind that it's very easy for the Starmie user to switch out and come back later and then take something down again, since Genesect can't switch into Starmie's Water STAB attacks. Furthermore, Starmie doesn't really mind paralysis from Jirachi's Body Slam and since you lack Protect you will have a hard time recovering from Rain boosted Hydro Pumps. I think you should be using Latias instead of Reuniclus. While Latias may not be the best Starmie counter around, it allows you to sponge Water STABs pretty well and then react accordingly. You can predict the following Ice Beam and switch to Genesect which will not take much damage from it, and then will be able to U-turn to give you momentum, using Starmie at your advantage. Latias is also an excellent answer to Keldeo, which is indeed something pretty rare in OU at the moment. Latias also has a role very similar to Reuniclus' except that it brings different advantage to the table, and in your team's case I think Latias' are much more helpful.
Quite honestly I would give Stealth Rock to Heatran instead of Taunt and use Protect instead on Jirachi. Heatran is still one of the most reliable SR setter in the metagame with its great typing and offensive presence that will cause a lot of switches, giving you many free turns. On the other hand, Protect on Jirachi gives it more reliable recovery from Wish, which is going to be crucial in games where you need Jirachi the most as it seems to be your main defensive backbone. Regarding Jirachi, you better switch these 32 Speed EVs to Defense instead, as it ensures Jirachi is NEVER 2HKOed by CB Haxorus' Outrage, as well as making it a bit bulkier in general, always nice. The extra Speed doesn't help at all as 244 is a dumb Speed tier in BW2 anyway.
Fire Fang is probably a much better option on CB Chomper than Stone Edge. EdgeQuake is pretty neat coverage but considering you have STAB Outrage to back up Earthquake you won't need Stone Edge at all. Fire Fang is pretty cool to have though, as Garchomp is going to lure in a lot of Skarmories willing to switch into Outrage / Earthquake, allowing you to catch them with a Super Effective hit on the switch. If you want to break walls with Chomper you better be ready to hit your main counter.
Anyway that's pretty much it, here's the set you should use:
EVs: 252 HP / 4 SpA / 252 Spe