My great grandmother is also Emma McCoy Clay but I have her mother as Martha Porter. Martha married Jesse McCoy 1n 1895, they had Emma in 1896. Emma was first married to Oscar Barber and they had my grandmother Bertha which means your grandfather is my grandmother's half brother. This time in our family history has been very difficult to research. Little is known about my grandmother's childhood or family because she didn't talk about it to anyone including her own children.
It's been 3 years since your post so I'm not sure you'll get this but if you do I'd love to hear of any information you might have gotten or stories you may have heard.
Hope to hear from you soon,