Eila doesn't read like
Isla to me. When I read it I think it should rhyme with
Kayla. I like the idea of using the last 4 letters of your mom's name but I would change the pronunciation to be more intuitive if it's the letters/spelling you're after.
Isla Claire would be nice.
Eila Claire, even pronounced the same, is more awkward because
Eila has all the letters of
Claire except the C. It looks redundant.
Eris Thorn looks cool, but
Eris makes me think 'goddess of discord' so I'd assume it was a girl (or more likely a female cat). I like the sound of
Eris for a boy though. Aerys maybe? I like Aerys Thorn too, but it is a lot less simple and everyone would assume it was from ASOIAF.