OP, regarding the 20-25 minute showers, here's what I did when visiting my parents and other siblings and in-laws were also staying in the house. I asked them, politely, to try taking a "navy" shower so that each person needing a shower would have hot water.
I was in the US Navy at the time. I explained to them that if they were to get into the shower and get wet, then turn the water off while they shampooed their hair, turned it on to rinse, and then shut it off again so that they could apply conditioner, etc., etc. I don't know if they followed my request, but I didn't hear anyone complaining that they'd run out of hot water, and I know that the water heater in that house would not support 15 minute showers for six adults.
It's just a suggestion to consider mentioning when you talk to him about the water getting on the floor. Good luck with the visit!