You've got some good advice on both sides of the question to help you in your decision. I had my son 3+years before his sister and his anger when she broke his constructions were far more intense than his reactions if anyone else had broken them. I wish I had created a safe place for his play, from his sister at the time. His sister, later-in-life, would get just as angry if she accidentally dislodged something another child had built. Her reaction was to then destroy the whole creation and hate herself. There may be no correlation to the two behaviors, but if you can give at least 5 minutes alone time with each IN the DAYTIME, I've heard it can make all the difference.
Both children (as well as myself) have later been diagnosed with ADHD/ ADD. We began medication when the quality of their life was no longer at a level any child should live through. They began to understand what part of their behavior and thoughts were due to chemical deficiency and what part of their behavior was by choice.
The correct levels of medication made it possible for them to accomplish what they knew in their head to be possible, but couldn't follow through like their friends and class mates seemed to be able to do...
At the same time, my husband has behaved very much like you have described your husband's behavior toward the children- and my ADD problems as well. The stress/anxiety level became toxic, and our son's reflective behavior (of the family's problems) helped us find a counselor who could address the ADD / nonADD+own issues- relationship that plagued our communications. Life isn't smooth, but we are committed to working this out- it's not one-sided.
There are resources out there for everyone. This is what I've learned:
(1) C.H.A.D.D. has support groups for the spouse of ADHD..bipolar adults are in the audience, they might be part of the support..., informative meetings for parents of ADHD...
(2) Sensory issues may complicate things, if he's not ready for kindergarten yet, keep him out one more year and go through Childfind at your school district - if he's having any sensory difficulties like playing on playground equipment or getting dressed or cutting with scissors, eating with utensils, or playing with playdough or fingerpaint, then they can help you (these are delays in self-help skills) as long as he isn't six, or in Kindergarten. Once he "crosses that line" they can only help you in the areas that cause an ACADEMIC delay.
(3) there is a book about how parents can work together to give children the "united front" for parenting: "Kids are Worth It" by Barbara Coloroso. It recognizes one parent might be extra harsh and the other, to balance things, responds more gently than they would've if the harsh response wasn't in their lives... and other parenting differences that really DON'T balance things, but .... well, I'm going to need to read it myself, but the person who recommended it was awesome.
(4) 5-7 year-olds do go through a stage of finding themselves belonging to the world around them, and they look for boundaries to control and be controlled that fit their understanding. If his behavior is just unsettling, "parent(verb)". If it's stressing you, "parent" AND make some changes, like investigating ADHD and scheduling routines + 1:1 time with each parent...
A comment based on an earlier response regarding labels and testing: Labels don't have to follow a child if they are only shared with the public to provide necessary funding and protect the child's rights (an I.E.P. or 504, etc.). There are tests for attention given after the questionnaires/ forms indicate ADHD. The child uses a timed computer response-program, then compare the result with the child repeating the same activity (on another day) with a small, short-acting amount of medication (only in their body for 4 hours). The focused activity comparison can give the questionnaires/ forms you fill out more confidence. When my daughter did it, she said, "the medicine I gave her helped her stop hitting and kicking when she was mad that afternoon..."
Finally, (5) You are a vital resource and parent in your children's lives. Keep in consistent touch with your resources, and network of support (DR.s, friends, medications, husband, personal time, etc.) and what your goals are in you and your family's life - and if your actions help those goals.
Keep up the good work! Your mind isn't lost, it's the stress to let you know changes in action need to take place.