general advice: use your fire types at the start of the fight and try to take out Gardevoir first; granbull is quite strong, but gardevoir has much better coverage; once whimsicott hits the field, bring out your steel types; whimsicott loves to use a prankster priority tailwind when it comes out, which will change the field to fairy-tale. Steel gets a nice power boost on this field, letting you eliminate any remaining threats. DO TAKE OUT MEGA MAWILE BEFORE THE FIELD CHANGE, AS FIRE MOVES BECOME DRAGON TYPE ON FAIRY FIELD, making it much harder to take her out without using a good ground type. Excadrill works wonders in this battle(but try to keep him for the second half; he doesnt last long), as well as Staraptor, since many of adriens pokes have a grass subtype. bringing your own terrain is also a valid strategy, but is not neccessary for victory. Dont try and force a poisin type on your team for just this battle (though crobat is an excellent option), as many poisin types that are avalible in reborn cant learn the moves they need to or are just bad.
For your team specifically, i could provide more strategy if you gave me your movesets and held items, but for what i can see now, i would suggest leading with noivern and your pick of swampert or torterra. priortize down the gardevoir, and actually hope that granbull takes out noivern; this allows a clean switch in for arcanine, who will take out mega mawile. togekiss is not particularly threatening, but is annoyingly bulky. try and use phyiscal moves against it. if you decide to use crobat, save it for when the field changes; poison is much less effective in misty terrain, as you cant inflict status conditions.