If I'm not mistaken, the legal guardian has the right to cease all treatment to a person in this condition if the person is not capable of speaking for themselves.
If I'm not mistaken - it is against the law to withhold water and food from a disabled person.
That comment reflects a mistake. The legal guardian has a DUTY to carry out the patient's wishes. If the patient's wishes aren't known, a court finds the patient's wishes and charges the guardian with the duty.
You are mistaken. The legal guardian has no rights vis-avis the ward. The state assumes those rights and grants authority to the legal guardian. The legal guardian must petition te court and receive authority to remove artificial life sustaining devices. The court is not supposed to grant that authority unless there is clear and convicing wvidence that is what the wards wishes were.
The power to remove the feeding tube has always been the courts and no one else's.