That's kind of a leap. Relatives can't put someone down. It has to be the wish of a terminally ill person.
See Halls at 91. You also seem unfamiliar with the Terri Schindler case, and a number of others of similar murderous result.
Tell that to Terri Schivo.
Who gets to decide what the patient's wish is? As we saw with Terri Schiavo, it isn't always the patient who decides. A rogue judge can easily decide that a patient wants to commit suicide, even when there is strong evidence against such a ruling.