Alright, besides having two pokemon with life orb, which you're gonna have to fix regardless of any advice I give, I might as well rate this team, right?
I'm not sure why you're using the EV spreads that you're using, so explaining those might be good (I'm gonna guess they are kinda standard smogon sets slightly adjusted for VGC or something but am too lazy to check).
I think that I want to start this off with saying that I do love the self-destruct + giratina combo. It is kind of predictable, but it is also just flat-out good. Being able to explode without fear of what happens to your teammate is a really nice feature to have. I think the core of this team is actually quite good, but I'd recommend some changes to capitalize on those best.
Anyway, I think that Mewtwo should definitely have some other attacking move instead of reflect; physical attacks are really rare in the VGC metagame, and taking a turn to protect against something rare is hardly ever worth it. I would highly recommend putting in Grass Knot over Reflect to deal heavy damage to non-scarf kyogres. Trick isn't worth it either; you don't have the time to pull it off effectively. I'd recommend using protect instead; protect is amazing in VGC and lets you get a free turn if you see a fake-out user. Also, clay isn't worth it, since games hardly last more than 6-7 turns anyway. I would much rather have focus sash (and protect makes this even more valuable, since they most likely won't flinch you turn 1).
I don't think that sleep-talk giratina is really appropriate for this metagame. I have seen more offensive giratina sets, such as ones with either choice scarf or lum berry (to guard against sleep from stuff like smeargle) used to greater effect. Not to mention that relying on hitting with a 75% accuracy move that deals slow damage and halves the less used attacking stat in the VGC game makes it not exactly ideal. I would recommend a set using shadow force, arguably one of the best moves in VGC (it attacks through protect, gets Same-type attack bonus, AND gives you a free turn of protection? Sign me up!). I have had personal success in using Shadow Force, Dragon Claw, Shadow Sneak, and Protect, and I'd probably use lum berry or leftovers with that (although sitrus berry gets an honorable mention). Smeargle leads are that much of a pain.
Aside from that, I have never really liked heatran, and none of your pokemon are weak to fire moves, so switching in heatran loses its strategic value. Not sure what I'd replace it with, though. All I know is that heatran really doesn't help your team out that much.
Latios looks fine enough to me; I don't see too many of those being used, but it certainly isn't bad by any means. I might recommend palkia instead merely because palkia is just that good, but I don't see any true problems with latios. It might not get enough time to use recover, so protect might be better than it, but besides that, the set looks good enough (although maybe use blizzard over thunder to take advantage if they use hail? I dunno)
As for the team as a whole, the leads do well against most trick room teams. Giratina is awesome against TR, since shadow force lets you stall it out, and explosion puts huge holes in their team even before needing to stall them. Add in light screen, and they're doing half of what they usually are, making stalling out the rest of it a piece of cake. This does well against most anti-meta teams, since all you really have to do is just get down a light screen and sweep as normal. Throwing protect on your back pokemon might be useful as well, since protect is a godly move in VGC, no lie. This plays as another goodstuffs team, since it seems to be based off of the idea of getting down a screen (quickly, since mewtwo is so fast), booming, and then letting your back sweepers take care of the rest, and since it's such a vague category, it depends from match-up to match-up.
While this team isn't perfect against rain, and heatran is pretty much rendered useless, it does have light screen, which helps a lot, as well as the fact that giratina resists water-typed attacks, as does latios. Latios seems to be there to help a lot against that (especially with both thunder and grass knot). However, you really don't have a good answer to ice-typed attacks at all besides, well, heatran. And heatran a. is weak to water, the most used type in vgc, b. is weak to fighting which is used a lot because of dialga being weak to it + hitmontops being really common, c. becomes largely useless if rain is up + you can't control the weather since you don't have groudon (but I dont think he fits on this team) and d. just generally kinda sucks in vgc And that's not good. Heatran is definitely the weak link on this team. I'd probably use something like metagross instead; it also gets explosion, it's bulky, it gets a lot of really cool moves including the priority bullet punch, and can also help take care of shedinja if need-be with rock slide, since with heatran gone you should probably prepare against that (and the move can flinch stuff that's slower, i guess, lol). Latios compliments it well since it resists everything that metagross is weak to, as well. It gives you flexibility for an item to use as well. Occa (resists fire), shuca (resists ground), and even passho (resists water if you want to fare better in rain or something) berries all work on it, in addition to leftovers, sitrus berry, or even lum berry if nothing else is using it. Metagross I think would be way better. Steel attacks hit super effective against abomasnow, which is something to keep in mind.
Besides that, I think this is actually the workings of a good team and I hope that I made it better!