Regarding Au Ra: In terms of writing, the implementation of Au Ra is...very clumsy. Their presence was essentially retconned into Eorzea.
That said, having an Au Ra be born in Limsa Lominsa is fine. It's worth noting that Eorzea knew that Au Ra existed and came from Othard before Heavensward, so while it would have been extremely rare at the time (although again, this might just be Square Enix's slipshod storytelling), it's workable.
One thing that helps is to have the timeline worked out.
For reference, the Garlean Empire invaded Othard in the year 1528 of the Sixth Astral Era. The Sixth Astral Era ended in the year 1572, and the current year is about ~6 in the Seventh Astral Era.
That means that there is roughly 50 years between when Garlemald invaded Othard and present day. We can assume that the Au Ra began to migrate to Eorzea as refugees anywhere within this timeline.
That said, having an Au Ra be born in Limsa Lominsa is fine. It's worth noting that Eorzea knew that Au Ra existed and came from Othard before Heavensward, so while it would have been extremely rare at the time (although again, this might just be Square Enix's slipshod storytelling), it's workable.
One thing that helps is to have the timeline worked out.
For reference, the Garlean Empire invaded Othard in the year 1528 of the Sixth Astral Era. The Sixth Astral Era ended in the year 1572, and the current year is about ~6 in the Seventh Astral Era.
That means that there is roughly 50 years between when Garlemald invaded Othard and present day. We can assume that the Au Ra began to migrate to Eorzea as refugees anywhere within this timeline.