Alan has given you the straight scoop.
What you have is a situation where someone in your home gave alcohol to two minors.Then, an adult relative of the minors intervened with the person who provided the alcohol, and a fight ensued.
If a local cop comes out to write a report because the parents or uncle are desirous of a complaint, they are going to spend days interviewing the minors, you, the man who provided, (handed the kids the shots) and the two who fought, and everbody else at the party.
The D.A. is going to look at this cluster, and going to try to determine if there is a crime here that he can convince a judge/jury to render a verdict of guilty on. The DA knows the guy who handed the kids the shots is going to want to file a battery complaint agains the uncle, and vice-versa. This is a tough case to make in a criminal court, but it sure as hell can be done, depending on lots of factors.
Now, in a civil case, the parents of the minors, (whom it sounds like were present at the party), share some responsibility for controlling thier children. The fact that alcohol was in the house is clear, the fact that somebody not the homeowner handed it to the children is clear, and if their is civil liability here I think it could go either way, a jury may fault the guy who handed the booze as primary, the homeowner as secondary, and the parents as at fault for not exercising suprvision.
Ideally, a group made up of somebody who can act like an adult from all involved corners, blessed with the authority to speak for their side, can sit down and talk this out, realizing that nobody really wins in these deals. Friendships have been ruined here already, the damage is done. Is it really going to serve to educate those kids and / or repair the other wounds by taking it into the legal system?
I think not.
However, you have to get people on a rational playing field if you hope to have them come to the same conclusion. Getting them therre might be the toughest move; I'd be on the phone to my attorney and my homeowners ins. co. ASAP to get them up to speed.