The defendants, while sympathetic, may believe that the ultimate responsibility of a child's safety and welfare belongs to the parent themselves. To the extent that the parents were aware the child was attending a party where alcohol was served, it was the parent's duties (Ryan's parents) to educate their child about the dangers of alcohol consumption and drinking and driving.
From a social perspective, perhaps, each of them should be liable to some degree, especially where there is an adult knowingly violating the teenage drinking law. There should have been a social obligation for these parents to abide by the law, even if not out of personal concern for the minor children.
Moral convictions might weight against the defendants. It would seem that just a common sense notion of human decency and caring for children should have compelled the defendants to be more concerned about a young person drinking and driving.
In your traditional case brief, you will not have this section. So, don't be confused or alarmed if you are unfamiliar with having this section in your case brief assignments. For my courses, I ask students to include this section for several reasons, the most important of which is that it is an exercise in critical thinking.
An essential aspect to critical thinking is being able to evaluate the same set of facts from different and diverse perspectives. This is a key skill in legal analysis, as you are tasked to think about the legal issues from not only your own or your client's perspective, but from that of opposing sides as well. This is necessary so that you understand both the strengths and weaknesses of a case. Moreover, it is a crucial aspect of demonstrating objectivity within the law. As sometimes no matter how passionate you and/or the client might be about a particular matter, if the law does not support the position, then you have to be able to see and explain that. The only way that you get to this understanding is being able to evaluate, articulate, and argue various perspectives. It is often very easy for us to argue and support our own opinions and beliefs. It is much more challenging task to understand and articulate those opinions and beliefs to which we are opposed and/or unaware.
In this section, you don't have to believe it. The task here is for you to be able to at least see the other possible perspectives, understand the legitimate arguments that might be made from those perspectives, and articulate those perspectives with the intellectual integrity and vigor they merit.