Dear JayPeeDee, when things turn "catastrophic" with a small child, it is often too late to turn back the clock. Your child is always in danger when he is left with her, as one can never trust an active alcoholic---she can't even trust herself.
I encourage you to make some changes for your son's sake immediately. I would n ever want you to suffer the pain of loosing a child--or having one maimed---when it can be prevented. You would have to live with that pain forever.
If you are willing to separate--as you mentioned above--the time is now. Luckily, you have the help of family.
I am speaking so bluntly because I believe that the welfare of your very vulnerable son is in imminent danger. Please do not take my statements as a personal criticism---they are not meant as such. I am trying to be supportive of you.
sincerely, dandylion