Hi Maxine, and welcome to the Forum, its good to have you here as well.
The usual medication used in the UK for worming poultry is Flubenvet. This is licensed for chickens and has no egg withdrawal problems. It's highly effective, and is given every 4-6 months from about 18 weeks old, so your POL girls could have it now, but the growers won't need it yet and are too young to be dosed with it. You can buy it on Amazon but am not sure if you can do this in France. It comes in a small light plastic pot, so if you have difficulty and have contacts back in the UK maybe they could post it to you. You just add it to weighed pellets using the scoop provided, mix carefully, and feed only those treated pellets for one week. Each bird then eats the right amount for her own weight and needs. Give no extras during the week or they will eat less of the feed. A potful will treat 20 full sized hens at the rate of about 1 kilo of feed each per week, so will last more than once with a small flock.
See the Poultrykeeper link on worming chickens http://poultrykeeper.com/general-chickens/worming-chickens
I don't know anything about Caprizole so can't advise. Don't rely on herbal tonics, they won't kill the worms effectively.
We do have another member in the Dordogne, Chrismahon, who usually posts regularly but ATM he's in England and offline for a while. When he returns I expect he can advise you about local drug provision.