It’s a parasite by the functional definition. The human fetus is wanted and that separates it from all the other parasites. As I have mentioned, only the host have the right to do whatever with it. If the fetus gets killed without the consent of the person carrying it then yes it should be a punishable crime.
Alzheimer is a degenerative disease and the life quality of patient suffering from it get decreased but I think it is not painful, I have not ever been in contact with a person with Alzheimer so can't say about the physical pain part. However, in my opinion if a person is in a vegitative condition then yes close relatives should be allowed to make a decision. Its is not an easy decision...my father still blam himself for convincing my grandpa to have the operation for his cancer. It was a fifty fity chance and my grand father was in pain beyond words. He did'nt survive , he would have died even with out the operation, a much painful death... but my father still feels its somehow his fault.