If it's serious fighting, I would forget using the spray bottle. I would separate the two cats into separate rooms of the house.
Serious fighting is when fur starts to fly, (literally), hissing, growling, really loud meows that's really penetrating and someone or all involved ends up being hurt.
Not-so-serious fighting has hissing and growling, batting and it's similiar to the above but the difference is that no one gets hurt and fur does not fly.
Since they are your cats, only you will be able to tell when it's getting dangerous and that's when you should separate them. And then let them be with each other after they have both calmed down and start playing with each other under the gap of the door.