I have a bowl full of waterfowl growers for the ducks and geese - mainly because that's what the geese were on before I got them and they're still young and needing to fill out. But the chickens can also access it, and do. Then I have layers pellets hanging up for the chickens which the ducks and geese rarely go near. I did contact Marriages to ask for advice and they said layers was actually the best solution for a mixed flock so once they all (or even any of them) start laying, I'll switch it all to layers.
As for the weather, today was the first day when my chickens wouldn't come out - normally in bad weather they'll dash out, get some food and head down to the goose shed (which is bigger and has an open door). Today two came out, didn't like the snow so headed straight back inside again.
H