I used to fish up that way quite a bit. Plenty of reef not too far out and some good wrecks also. Closest reef that is worth fishing (IMO) is Kolan Patch - about 15 km NE of Burnet Heads. There is also the '15 mile' and '17 mile' reefs heading E. A map with some generic marks used to be available from the local tackle shops, and that was what I used to get started. Not hard to find good ground from there.
If your brother has just bought the boat, make sure you have a good run in it in the river to make sure it is reliable and to become familiar with the handling before you head offshore and make sure you log on with the local VMR.