Amelia
Amelie
Emily
-- These are basically the same name. I don't really like any of them. There are hundreds of them in every playground.
Annabelle -- Like, but only spelled Annabel. It's too frilly spelled Annabelle.
Eleina -- Like Elena (without the I) and love Helena (which would go very well with Phoebe and Justin, which are Byzantine and Greek)
Ella
Ellie
-- Again, this is virtually the same name, and again, there are hundreds of them fighting with all the Amelia/Amelie/Emilys over the swings on a playground near you.
Imogen -- Don't like very much. Prefer Ingrid or Astrid.
Isabelle
Isobel
-- These are the same names, different spellings. There are not hundreds but thousands of them, duking it out with all the Ellies and Amelies. It's a nice name, imo, but way too popular.
Lily -- thousands of Lilys. Prefer Lilia.
Millie -- Very popular, and it's a nn rather than a name. It doesn't fit in with Justin and Phoebe because of that and also because it's a frilly name, whereas they're stylish.
Robyn -- nice
Rosa
Rosie
-- same name, pretty much. I prefer Rosa.
Sophie -- nice, but prefer Sophia. This is also a Greek name, so I think it would fit well with Justin and Phoebe.
Your DH has a one-track mind and lacks imagination where names are concerned, imo, but some of the names are nice. From the list, I like:
Annabel
Elena
Robyn
Rosa
Sophie
and the variants Helena (pronounced He-lay-na or He-lee-na) and Sophia.
Would your DH like:
Romy, Rosalie, Rosalind, Rosina
Lara, Clara, Laurel
Ingrid, Ines
Astrid, Annalise
Elizabeth, Eliza, Keziah, Dinah, Tabitha
Constance
I love the suggestions of Beatrice, Leah, Serena, Sylvie and Miranda, and I adore Zoe. I think it would be a fabulous name with Justin and Phoebe.