Can police enter your home without being invited in, without a search warrant? If so, under what circumstances?

If you are being arrested, do you have to be read your rights, or are there certain times when it is not necessary?

My brother is in jail right now, awaiting bail. He was having a dinner party with his girlfriend and 2 other couples, and there was a problem with the neighbor. In the hallway, the neighbor swung at him, and he swung back, and hit the guy, 2 times. The guy said he was going to call the police, and left.

When the police arrived they asked to enter the house, but the girl whose apartment it was said she didn't feel comfortable, and felt they needed a warrant to enter. The police said ok, just come outside we can talk about it. When they opened the door, eight officers in bullet proof vests rushed into the room and started assaulting my brother and his friends. They were handcuffed, and beaten. My brothers girlfriend was sleeping ans was awakened, handcuffed, and taken to the police station were she was stripped searched from the waist up. Everyone in the apartment went to jail. The three men all sustained some type of injury. They weren't read their rights, and weren't even told what they were being booked for until they were at the station.

This happened in South Bend, Indiana. Any help, insight, or advoce would be greatly appreciated.