I had another look into Hive D to see whether there was a Queen. I didn't see one but I might have missed her. I looked carefully for young but saw only honey and stored pollen.
My bee group have suggested that the swarm might have left their parent colony with a virgin Queen. In that case it could take time for her to mate and produce brood.
I decided to give the colony some choices so I put a frame of brood in from Hive C. There were eggs, young and sealed brood on the frame so, if there isn't a Queen, they can make one. If she is there then they've got extra bees to help them.
I gave careful thought to the risk of disease, given the local alert for AFB. Both colonies come from the same parent. Both have been given a week to use up the honey in their stomachs making comb. Neither show signs of AFB that I can recognise. I decided that the risk was sufficiently low to go ahead.