A gangster keen to keep street credibility and protect his boss who wants to go legit will do anything including killing the bosses son.

If the gangster from the original logline is a baddy, and the son has most of the screen time, try writing the logline from the son's POV.

"Protect his boss" is an open-ended goal. Typically, at the mid point this changes, and a more specific visual end goal is established.

Nir asked who the MC is. This is probably the most important question before moving to the next version of the logline.

So who is the MC?

The problem I am facing is it is an epic. Which means it is a story about a number of people against a backdrop.

The second in charge is the main motivator to story. But the son has most of the screen time. The boss is trying to build a legit empire, but his second in charge who is still very 'street' . He is keen to rule with an iron fist at the street level, which is undermining the boss.

When the bosses son gets in trouble the second in charge is willing to have him killed to be seen as tough.

These are a few beats, but there is a lot more happening.