that sounds like a lot to cope with.
I wonder if you've tried talking to your Mum about how this is affecting you all? Could you explain the impact her demands are having? Can your husband talk sensitively to her if it's too fraught between you at the moment?
I can't come to your Mum's defense per se, coz I don't know what she's going through at all, but as an MS'er I'm wondering if there are a few things going on for her right now that she may need some help or talking with? Do you have an MS-helpline or clinic where she could talk in privacy to them and maybe get stuff off her chest, or access appropriate resources or services? Sometimes when you lose control in your life you can come across as demanding, but it can be fear, grief, anger, depression, frustration etc....but like I said I don't want to presume to know what the issue is for her.
There could also be the situation that with a little one you are not getting enough sleep and rest yourself and your "fuse" is a bit shorter...that is not in any way a negative comment, but I can't take bad behaviour much when I'm tired either and I react quicker.
Also I don't know the situation in your country (I'm guessing US or Canada becuase you use the word "chores") but in Ireland you can apply to get some "home help" - a person to assist with shopping/cooking/cleaning for a few hours a week if you are below a certain income limit, or have an illness/disability - would there be anything like that in your community? It might give you a chance to rest, or even spend some quality time with your son, or Mum, and help ease the situation on you somewhat.
I really hope things improve for you soon.