They can decline the tests with respect to the breath and the police are able to search their coolers. The cooler search is not a 4th amendment violation and is probably done in response to safety concerns. If consent has already been given then it is too late. Perhaps alcohol or glass is prohibited on that particular beach.
In regards to your first question, if may depend on a couple of things. If the police had a report of underage persons drinking, then that would more than likely give them probable cause to search the coolers. On the other hand, and I can't imagine this is the case, but it could be, the city where the beach is located may have some rule about entering the beach and not having alcoholic beverages and their having the right to search. I don't know that that is the case and have never seen that, but just a thought.
As to the second test, I would say no, they were no required to submit to a breath test. Unless the officer had some reason to believe they were intoxicated, they do not have the right to test anyone at any time to see if they have been drinking. If someone had signs of intoxication, then probable cause might be established, but without those signs, testing people in this fashion is unconstitutional. They can decline the breath test. The officer has no right to arrest anyone without probable cause or issue a ticket. Therefore, there should be no consequences to declining to take a breath test where the officers have no reason to believe you are intoxicated.
They can ask for consent to search the coolers, but would need probable cause to "demand" that the coolers be opened. Got should hire a lawyer where the charges have been filed.
The officers can always ask for consent, and your daughter had the right to refuse. Whether or not the police had probable cause to conduct a search without her consent is going to depend on many unknown facts. Your daughter has the right to refuse the breath test without consequence, but they can still charge her with minor in possession of alcohol based on the circumstances alone even without a breath test.
James L. Yeargan, Jr. is licensed to practice law in the State of Georgia. All information given is based only on Georgia law, and is not directly applicable to any other jurisdictions, states, or districts. Any answer given assumes the person who asked the question holds a Georgia Drivers License, and this license is not a commercial drivers license (CDL). This response, or any response, is not legal advice. This response, or any response, does not create an attorney/client relationship. The response is in the form of legal education and is intended to provide general information. Any state specific concerns should be directed to an attorney who is licensed to practice law in that respective state.