MILs are hard to deal with as a general rule, esp the sons mother. Although yours is totally over the top!!!
I have a son, and i kind of understand why the mother gets upset, because its like someone took your son away from you and is the most important person to them now.
HOWEVER i look at it as that is just one more person to love and protect my son.
My MIL is hard to deal with, but not that bad our problem is that she wont pay any attention to our child but my SILs children are always getting attention, in fact, this is so crazy SIL is 33, and has two kids. She has NEVER once slept in a bed by herself, until she moved out to get married she and my MIL slept in the bed together. Well anyway, her husband got a job as a truck driver and is gone during the week, so my MIL has gone to stay with my SIL, because my SIL cant be alone!!!
So Sunday through wed they live at my SILs house then wed through friday, or saturday if her husband doesnt come home, they live at my inlaws house!!!
How freakign crazy is that!!! And my husband is gone on business and such all the time, he is right now, did anyway offer to come stay with me??? NO!!!!
Ok anyway, i digress, just wanted to show you that other peoples inlaws are crazy too,lol.
But your MIL sounds like she seriously needs some help. who brags about not taking care of their own children? why have them if you dont want to do anything with them?
If i were you i would just cut her out as much as possible.
Dont try to make your husband choose cause thats impossible for him, but tell him he needs to look at this and actually see how she is acting, not jusst how he wants to see her because she is his mom.