My Mom and sister took the train from the SF Bay Area to Orlando in 1983, with a stop in Washington DC. I recall that even though they basically spent more than a month on the trip, they still ended up flying from Orlando to New Orleans becuase the train schedule between these locales really didn't work out well. Of course, that was years ago and the schedules have undoubtedly changed.
As already pointed out, it will be more expensive than driving.
They will also need to pack their patience. Significant delays are common. This summer, on the first leg of my Mom's train trip from St. Louis to Washington DC, they ended up being bussed up to Chicago because otherwise they would have missed their train east from Chicago. Mom told me that the bus trip was horribly cramped and uncomfortable.
-- Suzanne