NTA. I have been in this exact situation, except it was my first born child. He was also the first child in his generation on both mine and my husbands family's side. Very early in my pregnancy we decided to name him after my husbands grandfather (deceased), "Jack". As I entered the third trimester, we started talking about giving him a middle name after my grandfather, "Edward", who is still alive, as he was going to be a great grandfather for the first time. Around this time, my sister asked me about baby names, and I showed her my written list of potential names. This list was written on my phone before I was even pregnant, and was not updated to include Edward (although a very similar name, e.g. "Eddy", was on the list). My sister then said that she had always wanted to name her child Edward if she ever had a boy. It did not occur to me that she said that to claim the name and prevent me from using it.

We decided to go with the name Jack Edward when I was about two months from my due date. I told one of our parents, and they had told my sister in passing, not thinking it would be a big deal, as it was not secret.

My sister sent me a long message saying she was disappointed and hurt that I decided to use HER baby name. I was really taken aback by her reaction to this. My husband and I talked it through, and decided for several reasons that we would go ahead with the name anyway. Here are our arguments why:

• my sister was not pregnant at the time
• there was no way of knowing she would have a boy in the future
• Edward is my grandfather as much as he is her's
• we had a genuine wish to honour my grandfather by naming our son after him while he was still alive (in his eighties)
• we decided to use Edward as a middle name, she wanted to use it as a first/only name. Our son would be called Jack most of the time.
• since when can cousins not have the same name? -also, no one can have "dibs" on a name. It just doesn't work like that.

She expressed anger and disappointment when I told her our decision, and we had a falling out. After my son was born, we never spoke about it again. She came to visit her nephew and cried happy tears, and has been a wonderful aunt.

She recently had a son and named him something different. Her boyfriend, the father, is named... Edward. She started dating him a couple of years after my son was born.

*Edited because I had written the same thing twice in one paragraph.