@Lawrence A. Kovacs III, Congratulations on an amazing goal.
There are many ways you can do this. I can advise on one way that long term will pay for both your father and your own retirement as it will give him the positive cash flow to live now while the properties are getting paid off to take care of your own retirement.
Step 1: Determine how much money per month your dad needs to retire.
Step 2: Determine his assets and liabilities. Does he have any pension funds he'll be able to draw cash out? Does he own a home that is paid off or with a small balance? If he's renting, will he still live there after retirement or where will he move and what will be his monthly rent & expenses?
Step 3: As he still works right now, can he take a mortgage and depending on what and if he owns any housing, can he buy a multiunit property with a 3.5% down, owner-occupied, FHA loan so he lives in a unit and rent the others to live for free?
Step 4: If you took care of his housing through either Step 2 or Step 3, can you either sell one of your properties or take a HELOC to pull out cash and buy investment properties that will give you enough positive cash flow that it covers your dad's expenses? - Bonus for you will be that while you'll be gifting your father your cash flow, you can use the Depreciation and tax deductions on this property or possible multiple properties to lower your own tax base, so you'll pay less income tax on your income while building your equity through the principal paid off by your tenants.
Good luck to you & your dad!