Can the brother or sister who live near their father be held criminally liable if he slowly starves?

Teresa, sometimes siblings don't help because they feel that their parent needs a higher level of skill. It's time to stop enabling Dad so that he keeps staying in his own house.

I see you are taking care of your Mom at your own home as she has Alzheimer's/Dementia. I assume that Dad is your step-Dad, correct? You mention "their Dad" and not "your Dad".

What are their Dad's health issues? Does he have memory issues and/or mobility issues? Can their Dad afford to pay a caregiver? Depending on his condition, he may qualify for Medicaid, to which he would be sent to a nursing home where he will receive around the clock care, and Medicaid will pay for everything.

Report his needs to adult protective services and ask them to do an assessment of his situation in light of what you have shared with us.