Based on the meanings I would go for the first. I think any variation of Mary is a beautiful name to give a child. Totally biased because Mary is a name I’d love to give a little girl.
Mared been the welsh version of Margaret - which I believe means Pearl. A pearl is a beautiful and precious thing, so very apt for a new baby girl. Second Choice.
I wouldn’t even consider Elan. It’s beautiful to the ear, but myself, I couldn’t name a child after a river. I realise you wouldn’t be specifically naming her after the river, but I believe meanings behind names are important. There isn’t any there.
Based on the sound, I skip Mair myself. The reason is that it My-er is the name of a major department store. To my ears it’s akin to naming your child Tesco! (If you don’t have Tesco in Wales, switch it with a big local department store that is in every shopping centre). Not a good name for a child. Since you aren’t Australian though, that isn’t really a concern.