when ADHD meets Autism

Both of my children have ADHD and neither of them take medication for it. My son is spacey but not real hyper, my daughter is not real spacey but is extremely hyper. They are now sharing a room. My daughter never stops talking, I mean literally she talks to herself when no one else is around, she drives my son nuts. He is Autistic and cannot process information very fast, he also cannot drown out background noise. My daughter not only talks ALL THE TIME she also talks very fast and processes information at lightening speed. My son cannot keep up and has a meltdown everyday because of my daughter. She is 2 years younger and doesn't seem to want to understand that she has to slow down for him, I have been trying to teach her forever to try and understand him. I don't think there is a diet or supplements in the world that will help the sibling rivalry syndrome. I am hoping that because they just have each other that they will come to be close as they get older. They do not have the option to only talk to certain siblings like I do. They are the only two.