So, after some observation, I think the squabbling between my two hens (Red and Blackie) was due to space issues when settling down to roost. I watched for a couple of nights, and Red is somewhat restless and takes awhile to decide where she wants to be for the night. I suspect this annoys the other two, who don't like being disturbed after they've flopped down for the night.
Unfortunately, they are regressing somewhat - I thought I had them well trained to perch at night and to stay out of the nestboxes. However, my Dad and have both caught Red in a nest box. Last night, both Red and Blackie were in the nestboxes. So, we made the decision to block the nestboxes off again (I'm hoping they'll lay there in the spring. Tonight when I came home, both Red and Blackie were laying in our shavings. I prodded them up onto the roost, and left when they all seem contented. I suspect this is their way of trying to solve the space issue.
Besides deciding this is a space issue, is there anything else I should rule out (red mites on our perch, or foot issues that would make it uncomfortable for them to perch)?
Does it harm an adult bird not to perch (I assume its better for them than just laying down, but now that I think of it, I can't say why)?
And I would appreciate your opinions - if it is a space issue, and my Dad is unwilling to allow me to hire someone to make a 3-4 coop, would it be kinder to rehome them? I would be sad to see them go, but maybe they would be better off in the long run. And my bargain with my parents was always that I was happy to take care of the hens, as long as they were doing well, but if they were not doing well, we would need to change things.