You'll be constrained on the sizes of the batches you can produce, but yes, a 12 quart pot can certainly work.
I comfortably get 6 lbs. of grain and two gallons of water in my 20 quart pot for my BIAB brews. I can brew up to about a 3 gallon all-grain batch of normal gravity wort (more if I do a partial mash and backfill with extract).
Given that your pot will be a little over half the size of mine, you should be able to mash 3 pounds of grain in a gallon of water, and produce 1.5 gallons of normal gravity wort using the BIAB process. Again, you can make larger batches if you do add extract and then top up with water in the fermentation vessel.
Fermenter #1 (6.5g): Empty
Fermenter #2 (6.5g): Biermuncher's Cream of Three Crops
Fermenter #3 & #4 (1.0g): Empty