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For the first, Isaac and Gavin both speak to me. I can't pinpoint why, but those just seem very apt.
For the second, I would be inclined towards Lachlan if he is similar to and gets along well with his siblings, and Jeremiah if he doesn't.
Best of luck :)
I love names that start with 'A' and 'M'. I'm always struggling to not give my characters too-similar sounding names.
And I always try to make sure that my character's name has a few different nicknames. Penelope James, for example, might be called Penny by her dad, Nelly by her friends, and PJ by her little brother. That sort of versatility really speaks to me, maybe because my name has no nn!
I have always thought of Elliot as a unisex name. It sounds good and is classy. I'd go for it, if that's the name that speaks to you. What middle names are you considering? If you give your daughter a very feminine middle name, that might alay any concerns.
Best of luck and congratulations!