you're better off feeding the laying hens Layers pellets/mash, with just treats of corn or whatever...
... the meat birds could be fed corn, or finishers pellets, or whatever.
so from this p.o.v. you need to be able to feed them separately.
fertilised eggs can be eaten, assuming they are fresh & kept cool!
We had kept all the young birds together, fed on Layers & some corn mixed in... and ate the cockerels when they became noisy, but if we were raising some just for meat, I imagine its worth thinking about you're feeding them - ours were'nt exactly overburdened with flesh! (but delicious!)