Think about it. People want the name of his brother, the child born just after Jacob. The very same person who about 30 years later died. So it doesn't matter if they named him Locke, Walt, Aaron or Vincent (
), the fact is that person is dead.
What people want is the name of the smoke monster itself.
This is my theory:
The smoke monster (separate entity to Jacobs brother) is like a car (sorry, can't think of a better analogy). Sitting in the light it is powerful yet useless without someone to control it....a driver if you will.
When Jacobs brother floats into the light, the smoke monster consumes his energy/life/soul/whatever and discards his body. That soul is now the "driver" of the car.
Now in the same way that a guy called Geoff owns a car, the car isn't called Geoff, it is Geoffs car. If Jacobs brother were called Tom, it wouldn't mean the smoke monster is called Tom, rather it would be Toms smoke monster. So his brother is controlling it, but they are two separate things.
When the monster talks about wanting to leave the island, again, if someone were inside a car and talked to you, it isn't the car talking to you, it's the person inside it.
Perhaps all the people it has consumed (Yemi, Christian, Locke) are other "passengers" in the vehicle/weapon and occasionally we hear their voices coming through as well as Jacobs brother (Locke and his don't tell me what I can't do).
To me this can end in a few ways:
1) The monster is somehow destroyed and all "occupants" are set free.
2) The "driver" is destroyed and another person takes control of the monster - Perhaps this is what Widmore wants...to destroy the current driver to take control of the monster himself
3) Jacobs brother gets what he wants, he leaves the island, perhaps still as the smoke monster, and setting in motion the island sinking that we saw in LA EX
I know this still has plot holes and discrepancies but lets face it, even the answer we get in the finale won't be watertight and will still have something for someone to pick at.
Let's be honest, if his brother were given the name Fred in the episode, immediately people would be on wikipedia looking for a link from Fred to an ancient Egyptian god or did Fred do anything in the bible. Perhaps TPTB thought that as the name isn't actually important, don't give him one as it will only be researched to shreds for no reason.
It might also explain why Richard only said "it's you" (or words to that effect) on seeing the monster as Locke. The monster doesn't have a name and that is what he was referring to, not Locke or Jacobs brother or anyone else.
My pennys worth anyway
One other thing, Jacob didn't kill his brother. More likely he was knocked unconscious when thrown to the ground and the water took him into the light where the monster killed him.