Poor hatch from our broody hens

We are getting very poor results from our broodys this year.  Some of the failures are infertile eggs and I guess our cockerel may be struggling to cover our twenty four hens.  We have also had lots of eggs developed but not hatched and I am wondering if this is to do with the dry weather.  I have built the nests with soil as usual but the soil is dryer this year.  Anyone else had similar experiences?  The last hen to hatch was distressing for me as she hatched some chicks but killed them all herself -young inexperienced mother I guess freaking out when the chicks appeared underneath her!!