Yes, it really is that easy. You will do what they call "pre-boarding", and you will sit in a separate area and enter the plane first. If you aren't checking any luggage, you can arrange this with the person at the gate ( the one at the little podium that everyone asks question). Otherwise, tell them at the ticket counter. We fly SWA all the time, and I have done this when flying with my 86 year old mother and with a friend who has trouble walking. There have never been any questions asked. Usually, tho, only one companion is allowed on with the person needing assistance, but if that person is assertive enough, they can hold seats for the rest of your party. Just remember to print your boarding passes online 24 hours befor your flight, and the will be the "A" group and board immediately after the preboards.
Kathy