Mixing 12 week old pullets with 24 week olds - What to feed?

[Eggcellent]

I have put two flocks of young birds together and there has been no agression issues or anything. My biggest concern now is - What do I feed a mixed flock like this? I do have oyster shell available on the side so could I just feed grower/finisher for another few months? The 24 week olds are banties and just started to lay eggs. Is flock raiser or even layer possibly better?

 

[HEChicken]

If it were me I'd leave them on the flock raiser and offer oyster shell free choice so the ones who are laying and need the extra calcium have it available.