When we were in our early teens, my sister and I used to argue over who would get to use the name Jack, as (a) we both loved it and (b) it's the name of our grandfather.
Well I say we would argue, my sister (who is younger than me) would be doing the shouting, I would be the one saying "it will simply be a case of who has a boy first."
Roll on a few years, and I fell pregnant at 19, and had a son. I named him Jack. Sister was furious.
Six years later, when pregnant with DS2, she tried to present DH and I with a list of names we were "forbidden" from using. We laughed at her and didn't even look at the list.
Lo and behold, the name we used (Alexander), was one of the names she wanted to "forbid" us from using.
DD's name (Sarah) also made her grumpy, as she liked that too.
We're both pregnant now - I'm due on 14 July - she's due on 19 August (her first child). We're both expecting girls. We have respectably agreed not to talk about names. If we use something she is considering, sparks will fly again, of that I'm sure.
But anyway, the gist of all that was, no-one can reserve names. It's a case of who gets there first in my book, and as far as my sister and I go, I have gotten there first. Just the way life goes I'm afraid.