First of all, let me say that I am very sorry to hear that your aunt has Parkinson's disease, and your grandmother has Alzheimer's. Both of these neurologic diseases can be very hard to deal/live with for both the patient and their families. As far as I know the short answer to your question is that Alzheimer's and Parkinson's disease are not directly related. That does not mean that you shouldn't talk to a neurologist
and get evaluated if you have concerns. Alzheimer's is an incurable neuro-degenerative disease first discovered by (and named after) the German pathologist
Alois Alzhemer in 1906. It is characterized pathologically by amyloid plaques and neurofibrillary tangles as well as a loss of neurons within the cerebral cortex. There is a (rare) form of Alzheimer's that is familial 50% of the time called early-onset Alzheimer dementia
in which it is diagnosed earlier than the age of 65 (usually diagnosed after this). Some theories on Alzheimer's think that there is an underproduction of a neurotransmitter acetycholine. Parkinson's disease on the other hand is a degenerative disorder which results from death of dopaminergic (different neurotransmitter) cells within the substantia nigra of the midbrain. Pathologic examination shows something called Lewy bodies. Thus they are two separate entities altogether. I would recommend making an appointment with a neurologist to discuss your concerns. I hope this information is helpful.