Dogs fighting

Dogs fighting

I have 3 australian shepherd, 2 males 5 and 1 years old, and 1 female 4 years old. I've had both males since they were 8 weeks and the female I adopted at 9 months. Shes always gotten along with my older male dog as well as other dogs she has come into contact with. Within the last few months her and my 1 year old male have started fighting. At first it seemed like when one was jealous of the other– one was getting more attention or fighting over a toy. But in the past couple days it has become more consistent with her attacking him for no obvious reason. Today my male 1 y/o dog came back home after being gone since the day before (I sent him home with my partner to give them their space) and she almost instantly went at him. He has grown up with her and theyve been best buddies and will play fight. Until recently their fights have been a month or 2 apart. Yesterday it escalated to the point of my partner being bit by her (on accident) when trying to break up their fight. Im not sure which course of action to take. They're both good, well behaved dogs and neither have a problem with my 5 year old male. She is spayed. Neither male is neutered. Thanks for the help!