After a vampire-supremacist wages a war to enslave humanity, his lieutenant, determined to stop him, partners with a celebrated vampire baroness to sabotage his faction through assassination, terrorism, and subterfuge.

I, like DPG, assumed the Baroness was human as well.
There is a fundamental flaw in the concept - when the stakes are an entire race being enslaved there is very little empathy available for the mere power play of a handful of enslavers.
Why not have a good guy or gal fighting for the freedom of humanity?

Clearer.

But it's not clear that any of them are fighting for the benefit of humanity. ?Who after all are the viewing audience.

It wouldn't matter if the film were like "Interview with a Vampire" ?where people are just occasional sources of food and a supply pool for new recruits. ? But in your story, the fate of the entire human race is at stake. And none of the 3 characters seem to be on their side, which is to say our side. ? They just seem to be fighting among themselves for power and whatever else vampires are in the habit of fighting for.
?
Consequently, there doesn't seem to be any character for an audience of homo sapiens to identify with or root for.

Why would I -- or any other homo sapiens -- want to care about who wins or loses, about the fate of anyone of these vampires? What's in it for non-bloodsucking people?

fwiw

Clearer.

But it's not clear that any of them are fighting for the benefit of humanity. ?Who after all are the viewing audience.

It wouldn't matter if the film were like "Interview with a Vampire" ?where people are just occasional sources of food and a supply pool for new recruits. ? But in your story, the fate of the entire human race is at stake. And none of the 3 characters seem to be on their side, which is to say our side. ? They just seem to be fighting among themselves for power and whatever else vampires are in the habit of fighting for.
?
Consequently, there doesn't seem to be any character for an audience of homo sapiens to identify with or root for.

Why would I -- or any other homo sapiens -- want to care about who wins or loses, about the fate of anyone of these vampires? What's in it for non-bloodsucking people?

fwiw