I'd be scared to death to feed corn meal. Granted, corn puts on weight, but I'd feed it cracked, not in meal firm, if at all. It's loaded with starch, so not a good feed, period.
Roundtable, good quality grass hay, is good. No stuffed in the world will put weight on if the roughage base is not covered.
Rice bran is good, you can feed a couple of lbs of that. I would add some alfalfa, either hay, or soaked pellets. Good protein and safe calories. A vit/ min supplement, maybe a probiotic, to help utilize the feed, or a ration balancer which contains all what's needed.
Have they been dewormed, especially for tape worm?
Nutrena has better feeds than the 12% and 14%, which are from the Triumph line, I assume. Try their SafeChoice, either the Senior or the Maintenance, if you want to feed a pellet.
I personally would go with the alfalfa pellets, rice bran, vit/min or RB, maybe add a handful of oats, and for the other one only a little of that, minus the rice bran.