I don't really understand this. You can't really get cold water in the system in August, the temperature below deck in confined spaces is nearly always above body temperature..hence you start with warm water. A little running of engines or genset in our trawler made for very hot water.
These days we have a small power cat, there is no hot water tank aboard. The transom shower is never "cool" . In a zero to 10 scale on an impediment to enjoying a trip to the BVI having 100 degree plus water and having 130 degree water I could see steam rising from would rank a 0.1 . There is so much to do and see and enjoy, as long as there are comfortable showers to be taken I don't believe many would view this as a huge problem. Heads not working? No water.. Big problem..By the way unless there was a watermaker on board, the person worring about long hot showers with 8 on board is likely to be unpopular. You had probably 200 gallon capacity. Though many don't abide by it, boat showers should conserve water. Get wet, shut off water, lather, rinse. Wet hair shut off water, shampoo rinse. In that case there is little difference in hot water or warm water. I am in no way saying someone cannot insist on all the hot water they want and as hot as they want. It is just not a big deal for most.

I'm not sure I understand the food situation. Did you hire the chef separately or furnished by charter co.? Did you provision the boat or did the chef? Did you tell them before hand that you wanted each couples food prepared separately ? Please correct me if that is not the case. In the small galley it would be somewhat unreasonable to expect the chef to prepare separate meals for each couple. I often hear of a person or couple aboard requiring different diets..vegetarian, gluten free etc..but I've never heard of three couples bringing separate food for someone to prepare individually.
Indeed when we had the charter boat and today at the condo down there we and guests will bring some special items from home..provision together and use the supplies in common. Since I have never heard of three couples wanting their food kept separate, I'm guessing the chef who has to plan the meals found it strange as well.
I'm sorry you had such a bad time but honestly can't understand it. Perhaps it would have been good to have told the chef that he/she was going to prepare meals separately with items each couple brought. That could have been discussed and the chef declined the charter or done it at a much higher per diem. Just my thoughts after spending trips on the water.