I suspect that you were charged with violation of Los Angeles Municipal Code 41.27 (c):
No person shall drink any malt, spirituous or vinous liquor containing more than one-half of one per cent of alcohol by volume, upon any street, sidewalk or parkway, park, playground, Los Angeles Memorial Coliseum, or in any railroad depot or bus station, or in any public place, or in any place open to the patronage of the public, which premises are not licensed for the consumption of such liquor on the premises.
You should steer clear of that lawyer you talked to as this charge is already only an infraction, not a misdemeanor! So, him wanting $2K to "kick it down" to an infraction is a scam!
The statements of codefendants are not likely to carry much weight in court. That 3 of you had no possession of alcohol is not clear at all! Just because the officer didn't see you physically chugging does nothing to "prove" that you were not in possession. The 4 of you were clearly a group and acting together. 1 of this group was seen actually holding and drinking alcohol, offering the alcohol to the rest of the group, and there was evidence of enough alcohol present to be shared by the group. Do a google search for the definition of "constructive possession."
In my opinion, you are not very likely to beat this charge. My advice would be to go to court and try to work out the lowest fine you can negotiate with the prosecutor (or the judge...I don't know if prosecutors actually work infraction court in LA).
That all depends on what "future career" you desire.