M.R.
It is extreemly common for parents of children with issues to need psychological help. EXTREMLY. Make an appointment for your husband with a psychiatrist, and get him the help he needs to deal with this. There are also caregiver classes though NAMI that will be helpful to both of you.
If the treatment plan for your son is not working, you need more help. If he is not getting hours a week of private therapy on top of the help he gets in school, he needs cognative behavioral therapy, social skills classes, medical therapy (access as often as he needs it until medication is working) speech and OT if needed. He should also have a developmental vision exam for motor and perceptual skills which are often comorbid and can cause homework refusal. Demand a functional behavioral assessment at school so that his homework issues become a school problem, not a home problem, and he needs a behavior plan for the "listening" issues that has only positvie behavioral interventions and supports. Go to www.wrightslaw.com to learn how to advocate for better serivces for your son, and supplement his school services with private serivces.
If you do not own your own evaluation, one with either a Developmental Pediatrician or a Neuropsychologist, then get one. Do not depend on the school to tell you what he needs, they are only there to make him funcitonal at school, you will need to provide private services such that his potential is maximized.
Read anything by Dr. Mel Levine or Dr. Russel Barkely. They explain the medical nature of ADHD and give great strategies that you can try.
This is hard work for the whole family. Seek help for the caregiver first...so that you can both help him, then get him much more help.
M.