Only a very select few private individuals can possess machine guns (
full-auto, select fire) in this state. The last count I heard was 52 individuals.
Essentially, all
semi-automatic AR15's with removable magazines, regardless of the manufacturer, are regarded as Assault Weapons in this state. Those that currently exist in CA had to have been registered with the DOJ either back in 1989 (Roberti & Roos) or 2000 (SB 23) to be legally possessed today. The only current exceptions are fixed or no-magazine lower receivers such as the FAB 10, DPMS, etc.
It's important that you and your brother go to the CA DOJ website and get familiar with the current CA laws before you possess or assemble an illegal weapon inside the state. These are felony offenses.
Go here.....
ag.ca.gov/firearms/. There is lots of depressing information on this site. This is not a fun place to live if you have an interest in firearms.