FYI:
My father was flooded (basement apt) and moved away for work...similar to what many in NO have done.
My grandparents have stayed and were flooded just in their basement....just inches below where the ground floor level was...very fortunate.
Your relatives sounded like they were fortunate. I saw some of the devastation, and it was pretty amazing to note the water line on some of the houses in the residential neighborhoods in GF. Some two story houses had waterlines near the roofline.