When two unlucky brothers are unable to pay off their dead father’s debt, they must fight against the Irish Mafia and the corrupt policemen who control the streets of Boston to protect their lives and take down the oldest organized crime group in the United States.

I found this version much better but there's still some work to do. I agree with the previous comment. I suggest you to do some research about the irish mafia and its peculiarities, you can maybe found what kind of event can put the story in motion.

One suggested alternative without knowing the story, based on Nir's comments:

When two brothers miss the deadline to pay off their dead father?s debt, they must fight against the Irish Mafia plus corrupt police who control the streets of Boston to ultimately dismantle the oldest organized crime group in the United States or die trying.

Same comments from the previous draft of this logline still apply:
Being unable to pay off a debt is a circumstance not an event.
What is the starting event of the story? What is the inciting incident?

The inciting incident needs to directly relate to their goal which is what by the way? Why do they actually need to take down the oldest organised crime group in the USA? What is at stake if they fail? What will happen if they succeed?

What does taking the organisation down mean? How will they know when they succeeded in doing so?
If it is putting the leader behind bars or killing him or her then specify this? Otherwise taking down is a generic and vague description of a goal.

Hope this helps.