So I take it the Rotom is causing you the most issues. Your delphox is so overleveled that I doubt it will be much help in this battle.
I'd level up your onix a bit as it is immune to Rotom's discharge and isn't too troubled by shadow ball. It will also help a bit with Chandelure but beware of energy ball.
Houndoom should make pretty quick work of Doublade so you should keep it alive for that (watch out for Brick Break). It can also help with Trevenant.
Mighteyena should help with Banette as it doesn't carry much to help with dark types (beware of destiny bond though).
I assume you can deal with Gengar as you make it to Rotom.
Overall your team doesn't have the best balance with 3 dark types, 2 fire types and minun (who is arguably the worst electric rodent out there). So training up some of those reserves for your team in the future wouldn't hurt.