This is a pretty solid Sunny Day team. I'd make a few small adjustments though:
-Overheat might do good on Ninetales. Since it's just there to set up the sun, it'll switch out pretty soon anyway. With the sun, it's pretty powerful. It rarely misses too.
-Will-O-wisp is kind of Risky on Ninetales considering its role on your team, perhaps swap it out for Solarbeam, but that's only minor. I assume this is just for crippling.
-Perhaps switch out Sludge bomb and replace it with Air Slash. It's still a pretty dependable move, it gets good power, and has a chance to flinch, which, paired with Crobat's high speed, is pretty handy.
-Overall, your team is powerful, but it's not very well prepared against other fire types. Aside from Darmataian, your team isn't well equipped against them (especially with a move like Flare Blitz, he wouldn't last very long for protection anyway), I'd have more ground and rock moves to fend them off. Flash fire could make it a bit painful for you.
-Personally, I'd throw in some STAB sun eruption, but it's not required. It does a ton of damage if the user is scarfed, but aqua jet still hurts.