I think aging parents are to be forgiven for their forgetfulness and their fear. I've been through this a couple of times and it's hard to reverse roles but that's what often happens.
What helped me was family support and sharing the responsibilities and visits. Also, there are some great support groups out there, the Alzheimer's Society could tell you of one in your area.
It's not codie to do for others what they cannot do for themselves. At that point it becomes compassion I think.
Hugs