My MIL has a grandson who is my nephew. She expected him to cut her 1 acre of grass, weed eat all around her house and rake the leaves. She never paid him a penny and then he moved to another town. Now she wants my son to do the same for her for free. Her theory is my son "owes her." My son has never asked her for money or for a ride anywhere, he has a job and doesn't cause me a moment's worth of trouble. Since my nephew moved away and quit mowing her lawn, my MIL bashes him terribly and vows to cut him out of her will. How would you handle this?

What does your spouse say about this? I would discuss this issue and your feelings on the issue, with your spouse and ask your spouse to protect your son, from his/her over-bearing mother.
I myself would never allow me or my child 2 b manipulated by a threat like being cut from the will... U give in to that kind of crap and u may as well turn in your "Self Respect" card.

Well when i was growing up you helped family or people to help, or because they were family not for money,i mean they offered a couple of dollars but we never took it, i picked coffee, fed chickens, calf, cow etc in Puerto Rico without expecting a dime, you arent teaching your son good values or to care for his elders, you are going to get old one day too. You dont have to have your son do it all the time but it would nice you can help too or your hubby and so what about her will are you depending or is he depending or waiting to benefit from the money from her will? let it go, its her money her will anyway........I wouldnt even "handle it" cause theres nothing to handle, i mean hello what ever happened to communicating to and with people? I mean i can see how you say she says her son owes her, may be true or not but its her opinion and that is something her son, your husband should address not you and funny cause i bet your husband isnt that worried about it like you are-

child labor laws.
i need money for my work done.
she should pay up

It is up to your son, if he wants to help her out, then he can have at it. If he wants to charge her, let him charge her. People don't really leave their grandchildren things anyways, they leave it to their children, it is up to them to leave it to the next generation. Let the grass go, or suggest she get goats.