Hey,
I'm not going to sit and insult name choices, but I've never been a fan of nicknames as names... Especially seeing that Jamie and James are the same name.
My brother and sister in law are calling their LO Olly, and I can't help but think they should call him Oliver officially and then just call him Olly anyway...
I do like the idea of calling him James on his birth certificate, and then calling him Jamie anyway. I think it's a good way of keeping your grandfather's name there and updating it to the only name you and OH can agree on!
By the way, I LOVE your girls name. A lady I know had her baby 6 months ago and called her Holly. It's strange because when I was at school there were people called Holly, but it seems to have fallen out of use now!
xx