Wow this is for in game :I
... Honestly I would rather not waste my time for in game EVs, but anyways: In game is all about hyperoffense, and bringing down your opponent faster. Rarely will you ever find the need for a bulky Pokemon, so you can go for a straight sweeper build on Gardevoir.
252 SpA / 252 Spe / 4 HP
For Salamence, this statement applies even more, the set for a mixed sweeper works here.
252 Atk / 252 Spe / 4 SpA
In game has no need advanced spreads (or any spreads at all) as you are not very likely to encounter the Pokemon that competitive players would expect. For eg.- EVing in special defense to take a Mega Charizard Y's Flamethrower is useless, because you will probably never see one in the game. Which is why I have kept the spreads simple.
Right, with that out of the way, here are the suggestions from the competitive point of view. As from what I've comprehended, your team is Blaziken, Mega Sableye, Gardevoir, Salamence, Kingdra and Metagross.
This team could possibly do well in Battle Spot, where only three Pokemon are allowed at one time, but during 6v6 it's clear that you have a huge weakness to Ghost and Fairy types. This is worsened when you consider that it's for wifi, where Mega Gengar and Mega Mawile are still prominent threats. Some Pokemon even run Dazzling Gleam for the sake of coverage against Dragon types.
The best set for Gardevoir would still stand to be then offensive set i.e the aforementioned spread. In fact, a Choice Scarf is even better, just because your team lacks the ability to outspeed some common threats, like Garchomp and some other mega evolutions. Scarf Gardevoir is a very good revenge killer, and it can also terminate many threats for your team (or even pull off a late game sweep, but only sometimes).
For Salamence, unless you go by Smogon (which I doubt since you are using a Blaziken) opt it as your Mega evolution. It somewhat gives a rest to your worries of the team being frail as well, and is probably the most used mega in wifi. Give it a bulky SubDance set (bulky with Substitute, Dragon Dance, Dragon Claw and Return):
252 Atk / 252 HP / 4 Spe
This set ensures that you can get up to four Substitutes up from full health, and still hit hard as a truck with Return. After about a Dragon Dance or two, you should be sweeping with ease.
Hope I helped!