I think it works for both. I've seen it mentioned as a girl's name recently, but it certainly fits the very popular boy's name style of Cayden/Jayden/Brayden/etc, so it feels pretty solidly neutral to me.
All your girl names are quite masculine traditionally .i Have never experienced Hayden as a girl name before . Here it's a pretty common boy name Especially in men in their 20s and 30s (80s 90s crop) I don't know about Finley as a girl either it is typically a male name anglicized from an Irish name meaning white worrier. (We are thinking of Fionn if we have a boy which means fair . So Been looking a lot into Irish names lol ) and Reece is anglicized form of Rhys it means enthusiasm. I've never loved it as a girls name and it is funny enough my husband's name ( original welsh spelling tho )
I'm also not a fan of sibling alliteration but that is just me and I know that a lot if people go that way
Finley was going to be our girl name and Finnegan our boy name, Finn for short. But once we found out we are having a girl Finley went out the window because I decided I wanted certain criteria for her name. I still really love Finley though.
Re: Thoughts on the name Hayden, and more...
Especially in men in their 20s and 30s (80s 90s crop)
I don't know about Finley as a girl either it is typically a male name anglicized from an Irish name meaning white worrier. (We are thinking of Fionn if we have a boy which means fair . So Been looking a lot into Irish names lol )
and Reece is anglicized form of Rhys it means enthusiasm. I've never loved it as a girls name and it is funny enough my husband's name ( original welsh spelling tho )
I'm also not a fan of sibling alliteration but that is just me and I know that a lot if people go that way