Mixed flock, ages, feed help!

I have a mixed flock of 5 adult hens, 2- 8month old roos, 1-8 month old pullet, two 12 week old pullets and 8-8month old guineas. I have been feeding meat chicken feed for the protein content along with free choice oyster shell for the laying hens. The hens are laying well with nice thick walled shells. All appear healthy, active, glossy feathers, pink combs, good weight. I recently had a 12 week old roo with Mareks, and a 7 month old hen die suddenly. Advice I received about the deaths included those that felt the diet might be to blame. So what should I feed? I know the 12 week olds shouldn't have layer feed, the guineas and buckeye chickens are supposed to have higher protein, and the hens need support for laying eggs. Should I feed flock raiser with oyster shells on the side? or should I feed layer feed for all of them. During good weather they free range, but we have had some frigid weather with heavy snows so they are confined to a coop with an enclosed run. HELP!

 

My coop is 12 x 10 with an attached outside run that is 10 x 11. I have 18 birds all together, and seem to get along fine.