It doesn't sound like a conversation with your mom is going to improve your relationship with her. Nor will it change her inablitity to be a good grandparent to your son. So, I encourage you not to have this conversation.
Instead spend some energy letting go of the fact that she will never be the parent or grandparent you want her to be. That's a loss. Grieve it and then let it go.
It may help to start addressing her by her first name. It can help you see her more as an adult you have a relationship with rather than a mother whom you have expectations of.
None of this means that you should stop protecting your son from her toxic behavior. That instinct is spot on and don't be afraid to follow it.
Your mother, however, may need some protecting from your kids too. As people get older their ability to handle disruption, noise, chaos, and even simple changes in routine can be a big, big challenge.
When we are in the thick of emotional family issues it can feel like all or nothing. But there is often a middle ground.
Maybe try this. Don't visit in November when your husband will be away hunting and not able to help. Go in summer when it's easy to be outside. Go for 3 days only. (Frankly I can't take family that I really like for much longer than that!) Stay in a hotel so that you can have control over how long everyone's together. You need that escape hatch with autistic children in even the best of situations. Plan outdoor activities that are not at you mother's home. Pic-nic at a park or play ground. Go where your son can be rambuncious at a distance and have freedom from the family pressure cooker. Make the event short. Or after an hour or two, have your husband take him away for one on one time. If there's something that your son excells at then maybe tie that in.
When your mother is critical just repeat a mantra to her every time. Maybe, "Parenting an autistic child is challenging. I'm happy with how things are going and we love him exactly as he is." Pick a phrase like that and repeat it over and over to any criticism.
All the things I mentioned above require a big critical shift in your thinking. You're at the point in life when you are not your mother's daughter. You are now the grown up in the room. As time goes on and her care needs increase you will have this role more and more. You will find yourself looking after the needs of your children and of your mother.
Protect your son. Manage your interactions with your mother. Ask for support from your husband. Take charge of the arrangements to make it more managable for all.
Your relationship with your mother will never be perfect. But you might be able to protect your son and still find a middle ground without throwing away your mother.
Remeber too that you are not alone in doing this dance. Many people struggle to navigate these kinds of situations.
Good luck and hang in there!
