Besides the noise violation which could be several hundred dollars, you could face criminal liability for furnishing alcohol to minors, and if someone were to drive after drinking at your party you could face what is called social host liability. The latter is a civil tort theiry best answered by a civil attorney. Bottom line is underage alcohol use could spell trouble for you.
Multiple loud parties could ultimately end up in a disturbing the peace citation, or worse arrest, which is very very rare. If drugs and/or underage drinking is going on, they you are responsible for the outcome of that. You could always check people's ID's if you are worried.
The next time the LAPD comes out the residence, they will likely issue a noise violation. If they drink, since they are in your house, you will be cited for furnishing alcohol to a minor. Since your parents own the home, they too can be charged and most likely will be charged.
Seth Weinstein, Esq.
Southern California Criminal Defense Attorney
This reply should NOT be considered a legal opinion of your case / inquiry. At this time I do not have sufficient factual/legal documentation to give a complete answer to your question and there may be more to the issues you raised then I have set out in my brief reply.