Backpackinglight has just started an article series on using large pots with lightweight backpacking stoves. Unfortunately, you have to be a BPL member (i.e., pay $$) to access the article. (Someone gifted me with a life membership; otherwise I wouldn't be there either.) To properly credit the source, it's here: "Lightweight Stove Systems for Group Cooking Part 1: Basic Framework for Selecting A Cooking Pot and Predicting Fuel Needs," by Ryan Jordan. BackpackingLight.com (ISSN 1537-0364).
http://www.backpackinglight.com/cgi-bin/...ml#.UozzzKVBVFw They used a 4 quart (1 gallon) pot, and, in 2 of the trials, the MSR WIndpro II stove I described above. (The third stove was a MSR Reactor system, which can't be used with more than a 2-quart pot, and the fourth was one developed by a BPL staff member and not on the market.) Interestingly, with the MSR Windpro II, the boil time was significantly improved and the efficiency very slightly improved when using the canister upside down (the cold weather liquid feed configuration).
Since the article looks at a 3-person party size, I'm not too sure it would be much help for a 12 person group. The results will be published in a week or two (depending on how many parts into which the article is divided). I'll report back if they come up with anything significant that would affect your group.
I suspect those leaky liquid fuel stoves can be repaired, especially if they are MSR stoves which I believe have a more or less permanent warranty (you'll have to pay for parts). However, that won't help the weight issue!
I'd be inclined to divide your group by 3 or 4, since no backpacking stove was designed for quantity cookery! If there are no older, more experienced Scouts to supervise each cooking group, then at least have as many stoves and pots as there are adults. How long did it take to boil that 2 gallons of water? And were 8 quarts sufficient for 13 people?