I think Delta Snorlax offers woefully little to your team, and if you’ve been struggling, it was probably because of him. It’s just a terrible Pokemon, not fast enough to use Belly Drum, and possessing no priority moves. He’d need level grinding to stay relevant. Grass as an offensive type is okay, but that’s literally all he has. The next best thing he has is Body Slam and… normal Snorlax can do his job better, come to think of it. At least the original Snorlax can use Curse + Rest to become a sweeper.
But if you really want to keep him, you should make adjustments to the trio of Dragonite + Delta Blastoise + Delta Charizard. They overlap a lot in both offensive and defensive capabilities. A Dark and a Ghost type Pokemon are awkward to have on one team, because both types are almost the exact same offensively.
It’s also awkward to have both Dragonite and Delta Charizard. Both are vulnerable to Ice, Fairy and Dragon attacks. These are 3 offensive types that grow more and more common and threatening as the game goes on. Delta Charizard’s Dragon Pulse is just too weak at this point, it just doesn’t live up to the pseudo-legendaries. You’d think Choice Specs would fix that problem, but Delta Charizard doesn’t learn enough good Special moves and isn’t fast enough to take advantage of that. Late-game Pokemon are relevant for one of two reasons: they have stats or abilities that make them hit really hard, or they learn a lot of great offensive moves allowing them to attack lots of people super-effectively. Non-mega Delta Charizard is neither of those. Shadow Ball + Dragon Pulse is pretty crap.
My advice would be to remove Delta Charizard entirely. Dragonite + Delta Blastoise work reasonably well, as long as you can protect your team against powerful Fairy-types like Xerneas and Mega Gardevoir. We’ll get onto that later.
Now let’s talk about moves. It’s unacceptable that Typhlosion has Blast Burn. The fact htat you have it tells me you’ve been playing him wrong. Hubris is one of the best abilities in the game, and Blast Burn puts that to waste by forcing you to wait a turn each time. Of course he won’t get as much done as a Mega Typhlosion should; he’s taking one turn’s hit each from every Pokemon he faces.
Train Typhlosion up to level 74 and teach him Eruption, or use Heart Scales to make him remember it. Also teach him Focus Blast, it’ll allow him to bypass Rock- and There is only one way to play Typhlosion against most strong trainers (gym leaders, ace trainers, etc.): eliminate most or all enemy Pokemon that will outspeed or resist a Mega Typhlosion. Then when a Pokemon weak to Typhlosion comes out, you send him out, and straight away start sweeping the team with Eruptions that grow uncontrollably strong.
Relearn Dragon Dance on Dragonite. Without Multiscale he won’t get to use it much but when he does, he can devastate the enemy team. Thunder Wave is useless on him.
Focus Blast is useless on Delta Blastoise. Replace it with Vacuum Wave to let it finish off speedy Pokemon.
Now what do you replace Delta Charizard with? You want one of those “Fairy Killer” Pokemon. That is to say, a Steel Pokemon–Poison Pokemon aren’t great because they tend to be weak to Special attacks, and Fairies tend to have a Psychic move. Metagross, Excadrill and Technician Scizor comes to mind. You could also do Magnezone, but it is pretty slow and vulnerable in the late-game. Magnezone could make a great complement to Mega Typhlosion once it learns Volt Switch. If you don’t mind waiting until the very late game, you could go with Genesect or Jirachi. And if you want to remove Delta Blastoise, Aegislash becomes by far the best candidate.
If it were up to me, I’d let Mega Typhlosion, Dragonite, Togekiss and Delta Blastoise stay. Kick out the other two, and bring in Choice Specs Delta Noivern, serving both as an excellent type complement to Mega Typhlosion and as a dedicated Fairy-killer. For the sixth slot I’d bring a bulky Water-type like Volcanion, Milotic, Palkia, Suicune, Manaphy, Rotom-Wash or Lapras. They resist Ice and Fire, both of which would be problematic otherwise. And Water-types tend to learn Ice Beam, which is great for all those Dragons you’ll encounter.
Finally, items. You should always make your Pokemon keep an item, even if it’s just a Lucky Egg or Amulet Coin. Togekiss might want Leftovers. Give Dragonite a Life Orb or a Leftovers (or a Choice item, if you don’t get Dragon Dance).