[name_f]Phoebe[/name_f] is least likely to have a nickname, the others it would seem likely since they are longer and have so many nickname options. I do see how [name_f]Phoebe[/name_f] might have to be crossed off though since it’s been used already.
[name_f][/name_f]I’d consider:
[name_f][/name_f][name_f]Daphne[/name_f] 
(she has similar sounds as [name_f]Phoebe[/name_f] and similar vibe as [name_f]Eloise[/name_f], is less likely to be nicknamed than your 3 syllable choices, and isn’t already the name of a family member. I feel like she’s perfect for you!)