Domestic violence legal in fl now?

My girlfriends brother was throwing rocks at her dog (animal abuse) and she told him to stop. Well this angered him so he threw a rock at her and hit her in the leg with it. She threw a rock and hit him in he head. and he chased after her and hit her (domestic violence). After she tried a second time to get away from him, he threw rocks at her (projecting a deadly missile i believe). Also, this happened while he was on probation his second time, one of the charges being for domestic violence (violation of probation). she showed the officer the marks on her, and the officer shrugged it off like it was nothing. The officer also told her it was a family problem and it just needed to be settled by her mom, and that if she would arrest anyone it would be my girlfriend. He has threatened to kill her and my family and me as well as their mom before numerous times. Her mom only cares about her son, and tries her hardest to stop the daughter from calling the police or if she already did, she will try her very best to get all charges directed at her daughter. So im assuming domenstic violence is legal in pasco county, FL now, and i am considering beating everyone that is related to me, that i am in a relationship with, that currently lives in my household and anything else pertaining to domestic violence. Disregarding my last remark, what can be done about this?