Don't be too surprised if the addition of the five does not help this problem. It is a good excuse to get more chickens so definitely use it. It may help. Depending on your set-up, I would expect the five new hens to hang as a group separate to your other flock. The rooster will still mate with them, but the ones that normally hang with him are better targets of opportunity so will still get most of his attention. There are a lot of things that go into bareback hens other than number of hens or hen-rooster ratio.
The one with the feather loss on the back of her head is probably due to the rooster grabbing hold and hanging on. The other two, I am not sure the rooster is the cause.
A couple of things come to mind. Are they molting? It is getting to that time of year. The normal pattern is to start around the head and neck, and progress from there. If they are molting, you should see a lot of feathers around.
Second question. Have you checked for mites and lice. For roost mites you have to check after dark since those mites hide during the day and attack at night.
As far as regrowing the feathers. If the feather is completely pulled out it should grow back. If the feather is broken off and some of the shaft is still there, it will not grow back until she molts or you pull the rest of the feather out. That is a big part of what molting is about, replacing damaged feathers.
If there are no big bare spots, it is probably not that big a deal. If you feel there is actual danger to your hens, you can use the search feature and read about saddles. They do help.
I don't know how old your rooster is. This type of behavior is typical of an adolescent rooster, especially with young pullets. Usually, not always but usually, their behavior will improve as they and the hens mature.
Good luck!
