The 3cs re alcoholism are again very much prescient:-
You did not cause this
You cannot control this
You cannot cure this
Why do you feel disgusted at feeling the ways you do; its perfectly understandable actually and not disgusting at all. Your mother's primary relationship is with drink and her main thoughts centre on where the next drink is going to come from.
If you can't look at her why would you want to at all subject your children to her as well?. Your mother is more often than not drunk; that's not nice for you to be around let alone your child. He is as you rightly state too young to be around this. So he should not be; you should stay away from her as well. Her "good days" are probably not as good as you think they are either; she is likely to be on a comedown from alcohol and is likely as well never fully sober.
Your children do not have to grow up around this; you have a choice here re your parents and your children do not. I would not let your dad off the hook here; he has enabled his wife here. They are currently together for their own reasons, they get what they each want from the relationship.
Re your comment:-
"Plus my dad would be devastated at losing out on time with his grand kids and would likely end in him leaving her".
Why would this happen, would he not ever want to see his grandchildren without his wife being present?. He could see them without his wife there. Has he actually mentioned anything to you about leaving her? If not that is mere supposition on your part.
Re this comment:-
"we've all spent years trying to support and help her whilst being understanding and to be perfectly honest I'm totally exhausted".
Alcoholism is truly a family disease that does not just affect the alcoholic;' the above is classic and shows how much you are all affected by this.
Your own process of recovery from your mother's alcoholism will only properly begin when you yourself decide to get off the merry go around and properly detach.
Those actions have been a fundamental error, you cannot rescue and or save people who do not want to be saved. She does not want your help or support and family members are the last ones who can help the alcoholic; you are all way too overinvested and mired in the alcoholic's problems. Like many posts of this type it is mainly about the alcoholic; everyone tiptoes around them.
You can only help your own self ultimately and a good step for you to take here would be to today contact Al-anon and read their literature. Your dad should do that as well as well as attending those meetings, they are very good with family members of problem drinkers.
www.al-anonuk.org.uk/
Confidential Helpline 020 7403 0888
(Helpline available 10 am - 10 pm, 365 days a year)