It may really be time to consider an alternative living situation for him, depending on his needs, Assisted Living, or Long Term Care. Your state agency that deals with the elderly may be able to help. Also, discuss this with his care provider (PCP) & your mother can talk with her doc/provider to find out what resources are out there. There are day care centers for the elderly like your father in some areas, and there are agencies that can provide caregivers; this may be covered by insurance to some extent.
I cared for my own mother for a long time, and having a break (for me it was adult day care) is necessary.