Why will my alpha hen not allow the other hens into the coop at any time? and how do i prevent this?

I am new to raising adult hens but it seems that the other 5 hens at different time will attempt to go into the coop to lay an egg, but the alpha will run in after them and chase them right back out. Also egg eating is a problem (i just put a seperate bowl full of oyster shells next to there feed).