Help Protect Max from His Abuser

Please help me keep my child’s abuser from getting access to him. Max’s father broke his arm out of frustration when Max was only 5 months old. At 8 months old he beat him with a bottle and threw him in his crib resulting in a week long hospital stay. Criminal charges were filed and he pled down to a class 6 felony child abuse with 5 years probation. Part of the terms of his probation is no contact with me or Max but I was just served court papers that he is suing me for joint custody. Max is now 3 years old with nonverbal autism. He CANNOT SPEAK. He has typical 3 year old behaviors, along with autism behaviors. His father has not seen him in 2 years. He doesn’t know him. He could not handle an infant, he cannot handle a 3 yr old with autism. Max cannot tell me if he is being harmed. I cannot let him get access to Max. I have 20 days to file a response or it will default in his favor and I cannot afford an attorney. Please, please help me protect my child.