Is there a girl code?

Ok! So I have a dilemma! My husband and I are expecting our second baby in November! We find out the gender in May. We been planning names since we found out! The names we have are Preston or Madelyn Jean. So my sister in law hears our girl name and got really upset because that's "her baby name" for when they have kids! (I've never heard her say that name before.. I've only heard her boy name which is Cooper. She has been trying to get pregnant for a while now (5+) years and apparently reserved those names! So I kinda sympathize with her and went with the back up of Ava Grace! Then my brothers fiancé who won't start to have kids till their 30 (they're both 21) said Ava Grace is similar to "her baby name" Avery Claire!

So now I'm just plain upset because I understand wanting a name, but my sis in law on my hubby side took our baby name and wasn't the least bit mad! She was pregnant first so she got the name!

Like I fell in love with Madelyn, and my brothers wife got really nasty angry with me saying " I guess we just have to rethink everything we planned for the last 10 years!"

So who's in the right? I know never to take cooper, but I never knew of her wanting Madelyn!!!