Mallory:
I posted a similar query earlier this year and was told to order some meals from Philmont to practice with. I have done this as well as bought retail Mountain House dehydrated meal packs. I've also used Oatmeal cooked in freezer bags. I taught our troop how to use the freezer bag method of cooking which requires NO water for cleaning… we simply throw away the dirty freezer bags. Spoons are licked clean and boiled at the next meal to sterilize them. This saves time, water, and fuel and lets us get away with smaller pots.
How are you going to rehydrate your food? In freezer bags? In a turkey bag? or were you planning to throw the food in the pots with the boiling water? This will directly affect the size pots you need to take.
For the sake of discussion, let's assume you will be rehydrating in freezer bags and won't need water to clean with:
Mountain House Retail Packs and Philmont meals usually require 3/4 to 1 cup of water per person. In a 12 person crew you would need up to 12 cups of water to rehydrate 1 entree for the whole crew. This is 3 quarts. You could conceivably get by with one stove and one 4 qt pot. Another more popular option is to use 2 stoves and two 2-3 qt pots. Instant oatmeal requires 1/2 cup boiling water per person so a crew of 12 would need 6 cups which is 1.5 quarts… only 1 stove with 1 2-qt pot would be needed to prepare oatmeal.
Now, if you don't use freezer bags to rehydrate in and eat out of then you will need hot water to wash bowls/plates. At Philmont, they teach using a 10qt pot to boil all the water for the meal and then tossing all the rehydrateable food in that pot. Then they have you use a separate 4qt pot to boil water to wash the pot and all the bowls and spoons. You can bypass cleaning a large pot by rehydrating in a turkey bag and serving the food out of that. Then you only have to clean the individual bowls/spoons and the serving spoon.
My recommendation is to at least TRY the freezer bag method of rehydrating with your Scouts. The scouts in my troop absolutely LOVED this method. If you do this, then you can get by with the MSR Reactor with the 2.5L pot and the Helios stove with a 2 or 3 liter pot. Our crew is currently using a Reactor stove with a 2.5L pot and an MSR Windpro stove with a 2qt pot. This is sufficient to provide enough hot water for a 12-person crew.