2 new chickens and 2 old ones and they pick feet

My neighbour got 2 new (grown) chickens and 2 which he had before. They can't stop them from picking each other pairs feet. As soon as they let them together they start. They have now separated them, but have no save enclosure for the "old" residents during the day.
Can anybody give them a hint how to make a "happy community"?

Thanks in Baz's the beeman's name (which is my neighbour) and he makes excellent honey!