Dad's dying from bile duct cancer&has reached stage where he's bed bound, not eating&has become confused.worried he's suffering.how long can this last?

Palliative care: I would recommend you to talk to his oncologist and ask for palliative care team/hospice care- to help him. Unfortunately , from your limited information, I do not expect this will last long. To make sure that he is not suffering etc- strongly consider hospice care.

Not long: If he is not eating or drinking, usually you pass on in a matter of days. Water is critical to survival. I am very sorry.