Rule #1: Never use two Mega Evolution per team. This is a waist of an extremely valuable item.
Delta Typhlosion is good only in Rain or New Moon centered teams, I highly recommend you get something else. I mean. for type synergy, regular Delta Typhlosion could be good, but it has a lot of competition with Magnezore who has superior bulk but lower speed. Having a rock resist would be nice for the team I will give you.
Delta Gardevoir is a decent Mega, but you need a lot of support for it to work effectively. I recommend using a Choice Scarf set instead, more on that later. Never use Thunder and Blizzard without their respective weather, Rain and Hail, or then use them strictly because you cannot acheive your goal without Thunderbolt.
The Mega Evolution I recomemnd you is Zebstrika, Manectric and Stunkfisk. Mega Zebstrika have the ability Competitive, so it get a +2 SpA boost every time an opponent lower its stats, can be via Intimidate or other moves. On top of that, it has very good speed in 116 Pre-Mega and 141 after Mega, meaning it is faster than a lot of things. Fairy typing is nice and it also have powerfull coverage in Overheat. Manectric has Intimidate and works really good as a cleaner and a pivot. It kinda does the same thing as Zebstrika. The reason to use Manectric over Zebstrika is Intimidate, more accessible Mega Stone and the more reliable Flamethrower. Stunkfisk is slow, but with Athenian, it does MASSIVE damage.
I recommend you to get into the safari and catch Thundurus. That will be very helpfull. Electrivire is A LOT worse than it seems.
Lanturn, sadly has 0 offensive potential, it has to be a support Pokémon. Usually, it is there for Mono-Water, but I can see it manage with our Electric team if it has Water Absorb.
On Rotom-W, seriously, Dark and Ghost have VERY redondant coverage. Do not use both togheter. I suggest you run Pain Split as your fourth move as a form of recovery, Will-o-Wisp or Thunder Wave.
As for Elektross, how about a physical Assault Vest set? It does wonders in PU.
Here is the team I recommend:
Zebstrika @ Zebstrikite
Ability: Motor Drive
EVs: 4 Def / 252 SpA / 252 Spe
IVs: 31 everywhere except Atk
Timid Nature
-Thunderbolt
-Overheat
-Dazzling Gleam
-Volt Switch
Gardevoir-Delta @ Choice Scarf
Ability: Clear Body
EVs: 252 SpA / 4 SpD / 252 Spe
IVs: 31 everywhere except Atk
Timid Nature
-Thunderbolt
-Ice Beam
-Moonblast
-Earth Power
Rotom-Wash @ Leftovers
Ability: Levitate
EVs: 252 HP / 248 Def / 8 Spe
IVs: 31 everywhere except Atk
Bold Nature
-Hydro Pump
-Volt Switch
-Pain Split
-Will-O-Wisp
Thundurus @ Leftovers
Ability: Prankster
EVs: 4 Def / 252 SpA / 252 Spe
IVs: 31 everywhere except Atk
Timid Nature
-Nasty Plot
-Thunderbolt
-Grass Knot / Sludge Wave
-Focus Blast
Eelektross @ Assault Vest
Ability: Levitate
EVs: 252 HP / 252 Atk / 4 SpD
IVs: 31 everywhere
Adamant Nature
-U-Turn
-Thunder Punch
-Drain Punch
-Knock Off
Typhlosion-Delta @ Life Orb
Ability: Motor Drive
EVs: 252 SpA / 4 SpD / 252 Spe
IVs: 31 everywhere except Atk
Timid Nature
-Thunderbolt
-Flash Canon
-Energy Ball
-Dark Pulse