Thank you for all the wonderful suggestions!
Greta Juliet -Juliet was a first name suggestion by my husband so it would be nice to have it as the middle.
Greta Jane - Jane is my middle name
Greta Starling - This one really grew on me. Cute bird themed middle name connection to big sis too.
Thanks again for all the suggestions! Now.... boy names... so much harder for me find one my husband and I can agree on. :)