I agree with what everyone else has said about a multi disciplinary team meeting about how to get family on board. But mum may be tired, and trying to change routine may seem to big a hill for her to climb. She will need the plan explaining and will need to be confident of support from all the agencies. Afterall any change in routine may not be accepted by the child for a long time. Even if it is possible for the child to reach these goals there is always alot of anxiety and stress around change for children.
Regarding communication through pointing at visual pictures. Can you try to do it starting from visual pictures for things he wants/needs/likes first. Always work through any interests the child has and on what communication problems are causing him the most frustration.
This is a very difficult situation. However, I assume some agency or school system has hired you to provide specific services to this child so I would contact my supervisor and share this information to see if there is any way you can get support for more parental involvement. It really depends, I expect, on whether you are expected to provide educational services or respite/custodial services. Good luck.
Wow. This sounds like a tough case. If this child's mother is not on board with what you are trying to help this child learn, then it is a no win situation. My best recommendation to you would be to get his "team" together to discuss what is going on with him. If that means the case manager, mobile therapist, or whoever is involved, they need to know and discuss this.
Another idea is for you to see how his school is handling his behaviors. It should be beneficial for both home and school to deal with this boy's issues in the same manner. Children with autism thrive in consistency. If his mother sees that they use a schedule in school, she may be more likely to implement that at home. Same may go for dealing with behaviors.