The question is not whether you want to retain your child in her grade or not. The question is what are the many problems your daughter faces and how best to address each.
Your problems are serious and I am sorry you find yourself where you are now. It is possible that your depression is the result of your years of frustration and failure.
May I start with your comment that you want what is best for your son. I also believe that his teacher and principal also want what is best for your son.