Marans are an amazing breed! Great layer of dark chocolate brown eggs! And lay they do! Hope it is a maran though the picture is not so clear... Show us the rest of the birds!
Definitely get rid of that rooster. They say the meanest roosters taste the best. So many very worthwhile roosters looking for good homes because the HOA or town codes prohibit them. After you acquire 20 posts, you can participate in the "Buy,sell,trade " forum. Often beautiful show or breeding quality cockerels are offered at very good prices.
I have three older hens that layed real good when i got them but now have started eatimg the eggs. Have tred oyster shell and grit nothing worked. Now i have them seperated from my news. Is there anything else i could try?