I need to help a senior passenger in a wheel chair from my car, through check in luggage, and to departure gate. I am driving my car so no handicap placard. He is departing from Terminal A. What is the best way to fo this

Most airlines will provide assistance for seniors and disabled passengers. You should call the airline for information. Otherwise you could unload your passenger and their luggage at the departing flights area. Can they sit by themselves inside the terminal for 20 minutes while you park in the hourly lot? You could then walk in to check them in and take them through security and to their gate.

You cannot personally do this. You will have to arrange for an airport employee to do be it

You can park your car at the hourly lot and proceed from there to the terminal or purchase personal assistance from the airline and just drop of the passenger at the terminal.