Hello there from a fellow UK resident and a fellow rescuer of ex batts. Well done you!
It is very rewarding to see the girls begin to flourish in their new environment but be warned....take it slow with them, it is a huge shock to their system when they first move in. Despite the horror of the battery life, it is very controlled....temperature controlled, light controlled, food controlled... so the sensory overload of their new found freedom can be enough to kill them. I say this from sad experience.
I'm sure the rescue centre would have advised you but....layer's mash to begin with, with a slow change to pellets. Not too many food treats until they are settled. They have trouble climbing and perching to begin with due to their weakened legs through lack of exercise so low perches and ramps into their house. Plenty of bedding to keep them warm as they usually have little feathering (though our current weather will help) and restrict their environment to the area directly outside their house until they feel safe and confident and have 'homed'...make sure they are all going to bed in the house every night of their own accord before you expand their range.
I wish you every luck with your new girls, welcome to the Yard and feel free to message me if you want any help or just someone to share with x