The chickens, the old pair and the new pair, seem to have finally settled down to a more peaceful co-existence. They arrived on the first bank holiday weekend in May, so that is about a month.
For a long time we were keeping them cooped next to each other but separate by day and then putting the young ones to sleep in boxes in our utility room. When possible, we would let them free range across the garden together but needed to avoid leaving them unsupervised in close conditions. Latterly, we started letting them have more time together during the day and taking the smallest one and one of the older, brown hens out in boxes at night. Finally we tried a couple of nights with both young ones and one of the older ones outside and, after all seemed okay in the morning, letting them all stay in the coop together.
As the person who lets them out almost every morning and puts them away many evenings, I am very relieved because it will save me time every day! Next, we have to work on raising the level of the pen because the two young ones can still get out despite having had their wings clipped (temporary solutions have been tried although they recently figured out that Mark I was rather flimsy and they could just jump through it!).