Both my brother and sister did the same thing to my mother which caused me to have "no contact" with them both for a very long time.
I'll preface this by saying that my mom is the most giving person in the world. She raised 3 kids after my dad left us over 10 years ago. She worked three jobs at one point just to pay rent for the shitty apartments she rented where she slept on the couch while she made sure we each had our own bed and space.
Now, my siblings, both happened to marry really shitty, crazy people. My brother in law says something one day during a conversation that turned into an argument. It was extremely rude and uncalled for and that argument perpetuated my brother in law cutting my mom off from seeing her grandchild. My mother missed her grandchild's first 3 years of her life because my sister didn't have the nerve to tell him to fuck off. My sister thought that standing by her husband due to an argument, that he escalated unnecessarily, was the right thing to do. I stopped talking to my sister for 3-4 years after that.
My brother's story goes about the same way. My mother helped them out as well because they could barely afford to make ends meet. Plus, they had a baby on the way also. (Babies seem to make people fucking stupid apparently.) My mother was paying the car insurance on the car that my brother was driving. She specifically told his wife that she could not drive the car because she was not on the insurance. Whatever, it was my mother's wishes. My mom doesn't have a lot of money and whatever little money she does have, she didn't want anything to happen (an accident) and have rates go up or whatever. Plus, IIRC, I'm pretty sure my brother's wife didn't have her license at the time anyway. All valid reasons for my mother to request that she does not drive the car.
Well, my sister in law thought my mother was being an awful person because they had a baby on the way and needed a car to get around with. They still had a car. Just not a car for whenever SHE wanted to use it. My brother could take care of things with the baby if needed. It wasn't anything that should've escalated to the levels it got to. The arguments caused them to stop talking to my mother and to stop letting her see her first grandchild. My mother was absolutely heartbroken.
I stopped talking to my brother and his wife for many years as well. I couldn't understand how these people who were being taken care of and given handouts were treating my mother so terribly. I stuck by my mother's side through all of these arguments. I tried to make my brother and sister see the error of their ways, but that just caused them to hate ME even more. So I stopped all contact with them for many years.
About 3 years ago we all decided that it was time to move on. My mother is in contact with her, now 2, grandchildren from my brother, and is even closer now with the grandchild from my sister. There is a bit of fear that my brother and sister will again try to hold the grandchildren over my mother's head and try to manipulate her. But, we just take things one day at a time. Holidays would go by where my mother wouldn't get to see one of her kids, or two. Now, every holiday we all get together and it's really a nice feeling. I think my brother and sister are crappy human beings, but if they make my mom happy that's all I care about.