A good approach to food stocks is to figure it out from what you regularly eat or from first principles of basic nutrition. If you go "fundamental calorie and carbohydrate/protein/fat" basis, your going to want to think 2500 or 3000 C (food or large calories) per person per day and 3000 Calories can easily be acheived in one to two lbs (nicely in a kilo) So you might expect that its going to be 400 to 600 lbs. Now very roughly, most dry food stuffs, and food oils are going to be about the same density as water… so viewing it two ways, you need around 10 cubic feet or about 12, 5 gallon buckets.
A full coat closet probably would hold it.......
For the shared storage area, you might try the "one mass too heavy to move", if you made a heavy duty "storage box" designed to be securly locked and put a two person supply there, together it would not be likly to walk off. this probably a 3 sheet of plywood sized project. say 8 ft x 2 ft x 2 ft.