I like
Eira, but not beth. I can't get behind it. Maybe with a different ending, like Eirabel or Eirabet or something. Just not
Beth. Its so lispy and frail to me.
I would pronounce it Ira-Beth.
If I were to spell it based on your pronunciation I would go with your spelling, Irabeth & Arabeth, depending if you are pronouncing it the second way you listed.