So, there’s some administrative stuff that needs to happen while the water is still up. First administrative concern is get in touch with your parent's homeowner's insurance agency and either: a) file a flood claim if they have flood insurance or b) get a written denial of claim form from them. The denial of claim form will enable them to apply for FEMA aid. The next piece of admin work is going to be finding a contractor. I would contact these categories of people in the following order (pretty much ordered by likelihood of being screwed over): 1) a disaster clean up company, like ServPro. 2) contractors local to your community (ask friends, look in flyers, google for them). 3) contractors not local to your community and possible not local to Houston. Getting a contractor is probably going to be the hardest part, so y'all should double or triple thread this effort. If you find a contractor, but they can't start until next week, reserve them but keep on looking. Don't stop until you can find someone that can start tomorrow. Lastly, how’s everyone’s cars? Do you have adequate transportation? If not, you need to find a rental car - I can’t tell you how critical this is. If you have total coverage on your car, there’s a good chance your insurance won’t cover a car rental, so this is likely to be a $1000+ expense that kind of creeps up on you just FYI.
For now, that should take care of the administrative stuff. This paragraph only applies if they can’t find industrial dehumidifiers which I doubt they’ll be able to do. When they get home, there is some physical stuff that y'all can do on their own. First off, check to see if the central HVAC system works. If it works, turn the fan on full blast and keep it running 24/7. I think it makes more sense to not turn the AC on because cold air won’t trap the moisture and our goal is to trap the moisture in the air then move the air outside. The flip side is that if you do cool the house down, mold will grow slower. I think the sweet spot is not letting your house get too hot because then it'll be a greenhouse, but not letting it get too cold because then the house will just stay damp. Second, open every enclosed space - all cabinets, closets, doors drawers, dishwashers, dryers, crawl spaces all of it needs opened. You really don’t want to open something after it’s had floodwater sitting in it for a week - take my word for it. Third, you need to buy and set-up any fans or blowers you can find. These will be hard to come by, but if you can find them, buy them. You're a chemical engineer, so figure out a way to set them up to get some airflow moving moisture out of your house.
After you have the “environment" stuff like that squared away, y'all need to start moving any fabric items out of the house. Those will retain moisture no matter how much airflow you have going. Every fabric-based item that got wet is a write-off. You should buy some heavy gloves and particulate masks, wear heavy shoes and just put in the muscle to move those outside onto the curb for trash pickup. The city will eventually come by with dump trucks and pick up all that stuff.
From there, it'll be contingent on if you were able to get a contractor. If you were able, they'll pull out your flooring and drywall. If not, you should think about starting that yourself. Flooring is pretty obvious but drywall is a little nuanced. Drywall comes in panels that are about 4(?) ft. high. The easiest way to rip out and replace drywall is to just pull out the drywall at the 4ft. mark - you’ll be able to just rip out entire panels and replace them with standard, un-modified panels from the hardware store. I've heard some insurance agencies will only pay to replace 2ft. of drywall if your house flooded a foot, but that's honestly just a ton of work because you have to cut the drywall to size on the demo and the re-build. If you have flood insurance, be sure to take pics before the demo and keep one board of drywall up so the adjustor can see how high the water came.
Getting through that will get you to next week. From there, you get to re-build and hopefully end up with a better house than you had before the flood, so there's the glass half full of all this.
More internally if you will, be sure to stay hydrated, fed and rested. This is a stressful situation, so you have to take care of yourself and try to stay healthy. Someone in my family got sick during both of our floods which just compounds a bad situation. Also, look out for the mental health of your family members. This ordeal is going to last way longer than you expect it to which really wears on people. A few weeks from now, someone may just get fed up with it and break down. Be there for them if it happens. Y’all’ll get through it eventually and things will return to normal - I promise. If you need anything else from me, message me here or text me at (512) 400-5274. Also, a shopping list will follow after this message.