A Mother's Options to Stop Her Childrens' Suffering

I heard a story on the radio yesterday that got me thinking. A mother has two children who were born with a degenerative disease, but this was not apparent until age 5. From birth to age 5, they developed totally normally but then slowly started to lose everything they had learned, such as how to walk and talk. I do not remember the name of this disease but it is extremely rare and also fatal. Their mother was told that they would not live past the age of 18. These two children are now in their 30s but they have been institutionalized for quite some time. They cannot do anything at all on their own and are fed through feeding tubes. The mother would like to end their lives to stop their suffering but both assisted suicide and euthanasia are illegal. She does have one legal option she could exercise -  she can have her children's feeding tubes removed and essentially legally starve them to death. She wants to end their suffering, but not by making them suffer even more. I just cannot fathom how ending someone's life by removing their feeding tube is legal, but humanely ending their life isn't.