Delta Gardevoir should use Choice Scarf alongside Thunderbolt, Ice Beam, Earth Power and Moonblast.
Good moveset for Spidergross is Earthquake, X-Scissor, Gunk Shot and your choice of Sticky Web, Knock Off, Superpower and Stealth Rock. This should be your Mega Evolution.
Delta Hydreigon should be run either Life Orb it Choice Specs with Hyper Voice, Earth Power, Fire Blast and another Coverage option.
To be honest, I don’t like regular Giratina. I highly recommend you fix that ground weakness problem as you kinda face a sand team. I would recommend using something like Defense Skarmory, Gyarados or another reliable ground immuned Pokémon. By the way, I designed an unusual Gyarados set that can help you destroy at least two elite four members.
Haxorus can be quite difficult to setup but is also effective. Use Dragon Dance, Earthquake, Dragon Claw/Outrage and Taunt/Poison Jab. Life Orb is prefered, although it can world with Focus Sash, Dragon Gem or Dragon Fang.
If your Blaziken does not have Speed Boost, then congrats on keeping it this far. Focus Sash or Life Orb is preferred too.