A young lawyer discovers through the diary of one of his ancestors that his family has served an ancient vampire for generations, so he must decide between succumbing to power and greed or doing the right thing and losing everything.

Thank you all very much for your input. How does it look like this?
A young mexican lawyer discovers through the diary of one of his ancestors that his family has served an ancient vampire for generations, so he seeks to break the contract so as not to become another servant of Count Vladimir.

1. Inject culture to set your story apart e.g. “A young Latino lawyer” - culture derived from your synopsis.
2. Usually, one human in vampire lore guards a vampire during the day known as a “human servant.” You can use my example or find another name from lore if going with the “must decide lawyer or human servant” route.
3. Concerning the lawyer’s life choice, it doesn’t appear he has one from the family's perspective – he must accept the calling. From the vampire’s perspective, he must approve. So, if your lawyer wanted out, he could sabotage the interview with the vampire.

Examples from Formula (link in header):
When a [CHARACTER], is [confronted by a MAJOR EVENT], s/he must [do the ACTION/GOAL].
or:
A [CHARACTER], must [do the ACTION/GOAL] when [a MAJOR EVENT occurs].
“A promising young Latino lawyer must decide between [lawyers non-vamp path e.g., true love] and [lawyers vamp path e.g., old-money family inheritance] when Count Vladimir arrives in Mexico to interview his human servant heir”

Kept the name “Count Vladimir” in the logline as I believe the reader will “get it” based on his purpose.

Keep going!

"...helping him turn an entire nation into his hunting ground.." makes the antagonist oiut of him.

That's better. How about:

When he discovers his family has served an ancient vampire for generations a young Lawyer must... (Then tell us what he must do)

You´re right, thanks. how about this? A young lawyer discovers through the diary of one of his ancestors that his family has served an ancient vampire for generations, helping him turn an entire nation into his hunting ground.

I would avoid loglines that end with a choice. Because watching a 90 movie where the lead is like "Should I?" or "Shouldn't I?" Makes the lead seem indecisive. Besides 90 minutes of someone trying to make a decision isn't very compelling.

Instead, I would have the lead be 'Trapped'

The lead discovers he is bound by a contract his ancestors made and the story would be him trying to figure a way out.

Dig your lead into a hole then start shoveling dirt on top of him.