This mare looks as though she could be in foal. Is this the younger mare? If so, are you sure about her age as she looks a bit immature in the pictures. How tall is she and how big is your stallion and is he a refined type or more substantial in build?
Sorry for all the questions but it will help those here when giving advice. Pictures would also help.
You need to check on your mares udders - any SLIGHT filling will give you an idea that they are approximately 4 weeks away from foaling, depending upon your feeding programme. They will need a good quality mare and foal feed during those last weeks and after foaling, plus it is a good idea to give a wormer a month (4 weeks) before foaling, plus have a word with your vet about bringing their immunisation injections up to date at this time. But do keep checking those udders so you can make arrangements for your girls to be on a 24 hour watch as they get closer to the event - it is really vital that you do your very best to be with them as they foal!