Well first things first, evolve that Growlithe with a fire stone. One can be found in Mount Pyrous
Start around 10:45 or so.
Also, do you really want to use 3 fire types, it's kind of redundant unless you're doing a monotype. If you can find any other move for Seaking other than Horn Drill do so, because it's too unreliable. Get a heart scale and go to Onyx Ward and teach Venomoth Quiver Dance. Cofagrigus will be a great party member in this battle. I'd swap out Fearow for it, but train it up to level 53 or so, make sure it knows Will-O-Wisp and it will be a good lead against Cincinno.
What are the abilities on Blaziken and Growlithe? You can find Ability Capsules in some place which would allow you to change their abilities to Speed Boost and Intimidate respectfully, if you can get your hands on one. Save before using it so you can reset if you don't get the abilities you want.