I have 6 chickens. Betty and Barb about 18months old - isa browns, Rhonda and Renae 10months old Pekin Bantums and I have just got two pullets Mags and Marg 14 weeks old - Isa brown/rhode Island. the two bantums lay everyday/second day however Betty and Barb stopped laying for a while (Winter) they have started laying again however very soft egg shells - probably once a week. I have a mixed grain food, tub of shell grit in pen. I worm and de-mite them. Sometimes the eggs are still formed however very soft but most of the time the soft shells are left in their laying box broken. Are there any suggestions? They all appear to be happy little chickens - are free range - eating, drinking, scratching. Scraps given every second day. Thanks for your time. Regards.