Hey malomyotismon i got your request!
This team seems pretty cool. Using both Latias and Latios on the same team seems pretty creative and the use of Cobalion is also a nice suprise. However this team does seem to have trouble with a few pokemon. Volcarona stands out as a big offensive threat, although you have Terrakion who can revenge kill it every other pokemon on your team is outsped by +1 offensive Volcarona and is hit super effetcively by Fire Blast / Bug Buzz / Giga Drain. Also if Terrakion has just revenge killed something with Close Combat Volcarona can come in and easily get a Quiver Dance up on Terrakion and with Terrakion switched out nothing is stopping Volcarona from getting up two Quiver Dances. Cobalion will then be outspeed and Volcarona resists all his moves but Volt Switch which won't be doing much after 2 Quiver Dances, Volcarona can also get up a second Quiver Dance on Rotom-W making his Hydro Pump easier to take while Volcarona can just heal up by using Giga Drain, Latios and Latias are in the same boat as Rotom-W in that after a Quiver Dance Volcarona outspeeds and can set up another one to take less damage from their attacks, or if Terrakion is gone just outright sweep your team. Rock Polish Landorus also looks like quite a threat while it might not be able to muscle past Latias or Rotom-W when they are healthy Rock Polish Landorus is found on a lot of hyper offense teams and sand offense teams which can wear down Latias and Rotom-W with hazards and residual damage. Latias can also be Pursuit trapped by Tyranitar opening up a Rock Polish Landorus sweep. You mentioned Deoxys-D to be annoying because it can get up hazards easily and it is often paired with Rock Polish Landorus on hyper offense teams. After a Rock Polish, Landorus outspeeds your whole team and can hit all but Rotom-W super effectively with Earthpower / Focus Blast / Hidden Power [Ice]. Dugtrio can trap both of your Steel-types making it a pain to handle because without your Cobalion or Jirachi your team is very weak to Dragon-types like Dragonite, Haxorus and even opposing Latios and Latias. SubDisable Gengar is another fast special attacker that your team has trouble with. It can hit your whole team super effectivly with Shadow Ball and Focus Blast while it can also speed tie with the Lati twins. If it is behind a Substitute it can also wreck Terrakion with Focus Blast or screw it up with Disable. Just like Landorus, Gengar is another pokemon commonly found on Deoxys-D hyper offense teams which makes Gengar even harder to deal with. Focus Sash Alakazam is in the same boat as Gengar pretty much being able to hit every member on your team super effectivly with Shadow Ball and Focus Blast aside from Jirachi and Rotom-W. Varaints that carry Energy Ball can also hit Rotom-W super effectivly and Alakazam can use Psychic/Psyshock to deal with Terrakion as apposed to the much more unrelaible Focus Blast. He also outspeeds your whole team barring Terrakion who he can revenge kill if his Focus Sash is still intact.
To help you against some of these problematic special attackers i suggest Bronzong>Jirachi with Levitate Bronzong is a great pokemon to have in your team and lets him wall Landorus and avoid being trapped by Dugtrio two things that Jirachi can't do and two things that are very important seeing as Rock Polish Landorus is a huge threat to your team and if Jirachi is trapped by Dugtrio your team is more prone to being swept by Dragon-types or strong special attackers like Gengar or Alakazam. With its great defences Bronzong is capable of switching into the special attackers that threaten your team and beat them. With acces to Hidden Power [Ice] Bronzong is a great answer to Dragon-types, Gliscor and more importantly Landorus. Gyro Ball combined with Bronzongs base 33 speed and respectable base 85 attack let it dish out a suprising amount of damage and helps you beat Gengar and Alakazam. The move also hits Dugtrio super effectivly letting you deal with him easier as well. With Stealth Rock on Cobalion there is a free spot on Bronzongs move set. You could opt for Psyshic to hit Gengar super effectivly which is quite nice if it Disables your Gyro Ball, while Psychic is also useful for hitting Fighting-types super effectivly which are very common in the current OU metagame. Toxic can also be used to cripple switch ins like bulky waters. Bronzongs last move is Earthquke which is a good move to use on Tyranitar who threatens your Lati twins but its main purpose is to avoid being trapped by Magnezone. 2 ivs are used in speed to give Bronzong quite a powerful Gyro Ball while also giving him the ivs necassary for Hidden Power [Ice]. You shouldn't really miss Jirachi to much with Bronzong seeing as they have similar qaulities (same typing good defences) the difference here is that Bronzong has Levitate and Gyro Ball letting it take on Landorus, Gengar and Alakazam easier while also being able to avoid Dugtrio.
Although the theme of your team is to use both Latios and Latias i think having both of them running a Life Orb set is a little redundant. Additionally if you decide to go with my Bronzong you would of lost your Jirachi meaning your team is without a set up sweeper. Thats why a Sub+CM Latias>Life Orb Latias would be a great idea. With Calm Mind boosting Latias's special defence and special attack Latias can give your team a great late game sweeper in Jirachis place. I suggested the Substitute set because with Latios already having better coverage then any other set Latias can run, Latias doesn't really need the coverage while Substitute on the other hand is a great move to block harmful status that is commonly aimed Latias's way such as a Thunder Wave or a Toxic. Substitute also protects Latias from Scald burns letting him set up on bulky waters like Jellicent, Vaporeon, Gastrodon, Politoed lacking Encore/Perish Song, etc. Max Hp and Spe are used to give Latias great bulk and the ability to get up a fast Substitute and make the most of his fantastic speed tier. The loss of Latias's Life Orb set isn't an isue with Latios preforiming an almost identical role albiet being a bit more offensive and less defensive. On the other hand your team would really appreciate the sweeping potential that Latias brings to the table.
With these changes i feel like your team is much more solid however Volcarona is still a big threat to your team. To help your team better deal with Volcarona i suggest Thunder Wave>Will-o-Wisp on Rotom-W. Thunder Wave is awesome to cripple Volcarona and reduce its speed making it impossible for Volcarona to get a sweep. Also a paralyzed Volcarona will always be outsped by Terrakion letting you revenge kill it easy. Thunder Wave also works great by slowing down other fast special attackers that gave this team trouble like Alakazam and Gengar. Thunder Wave on Rotom-W fits perfectly with my previous suggestion of Sub+CM Latias. Having a lot of experience using Latias i can say that a Thunder Wave'd opponent is very easy for Latias to set up on with the 25% chance not to move letting Latias Recover/Calm Mind/Substitute much easier. Speaking of your Rotom-W you are missing 12 evs on it which i suggest dumping into special defence. Another change to help you with Volcarona is Rock Slide>Secret Sword on Terrakion. Stone Edges 80% miss rate is often quite unreliable and for your team you really can't afford it to miss when you are in on a Volcarona. Rock Slide on the other hand while being less powerful then Stone Edge has a much higher accuracy and still hits Volcarona 4x effectivly letting you ohko it much more reliably the Stone Edge. Secret Sword is a good move, but it is not really essential on Terrakion especially seeing as Close Combat is much stronger (although Secret Sword does have the advantage of defence drop).
Good luck with the team i hope i helped!