Assault charges for something that wasent intentional?

over the 4th of July weekend my brother and other family was over. our neihbors were shooting guns and it was pissing us off. we asked them to stop and they didn't. so we called the police. one shot actually hit my garage side door and I believe was done on purpose. so my brother threw a m-80 firecracker in their yard because he was pissed off. the man next door didn't enjoy it and threw a string of firecrackers in my yard right where we were all sitting!!! after my brother yelled curse words and yelled at the man the man next door ran and hopped the fence into my yard, him and my brother engaged in a fist fight and my brother beat his ***. I think his nose was broken and he was bruised badly. shortly after the police finally arrived and arrested my brother because the man next door pressed charges and claimed he didn't do anything and

my brother just ran next door and fought him which was a lie. what can my brother do? is he going to prison? what are the charges?