I mean can they look in the windows and demand to come in when they had no proof anyone was underage? (No one was...) Someone told the cops they could not come in without a warrant, the cop asked him for ID and put him in handcuffs for obstruction of justice. They were looking over a fence in the backyard through the back door.
If they were there pursuant to a complaint then looking in a window is not a search.
Next we address the entry, IF entry was given pursuant to an order or show of authority, even if resisted by you, then this may come into question if it was a consensual entry or not, your attorney will be able to sort out state case law.
IF you resisted, and they came in regardless, then the question is, was the warrantless entry valid?? It is possible it was, yes, as if alleged underage persons were on the premises, it could present a warrant time frame issue and approval. Alcohol poisioning by minors can happen sometimes quickly before action can be taken by the police, courts will then look to see if the emergency/exigency bypass of a warrant was appropriate.