Think if I was going to try something like that I would try slipping the chicks under the mother hen under cover of darkness then they are just 'there' when she wakes up, if she is a placid hen it could work. As for the feeding, think maybe the younger ones should stay on the chick crumb for the required amount of time, if you give creatures a good start they stand the best chance of maturing into good adults, I am sure I have seen small 5kg bags of chick crumb probably in Pets at Home but must be available elsewhere, by the time you wean them from crumb onto growers surely there wont be much wastage ?