As you have so many people to honour, perhaps prioritising your mother and grandmothers would be useful, this time around at least?
Some ideas anyway for versions of your aunts names (although I like the originals a lot, too) :
[name]Eleni[/name] - [name]Eleanor/name, [name]Eloise[/name], [name]Elodie[/name], [name]Helen/name
[name]Zahara[/name] - [name]Zara[/name]
[name]Arete[/name] (I adore this one - perhaps in middle place?) - [name]Harriet[/name].
Panayio could become [name]Pandora[/name], Pandia or [name]Pansy[/name] (although that one is old-fashioned, undesirable slang).
While [name]Stella[/name] is having a resurgence, along with many other vintage names, I don’t think it is too trendy at all, especially as it is to honour family. You could also use [name]Estelle[/name]/a, or any other -elle name, such as [name]Arabella[/name] or [name]Giselle[/name]. These could honour [name]Eleni[/name], too. Another name meaning star, such as [name]Tara[/name], would also be an option.
Are too middle names a possibility? To honour everyone? If so, perhaps :
[name]Frederica[/name] [name]Estelle[/name] Panayio
[name]Estelle[/name] [name]Pandora[/name] [name]Frederique[/name].
I don’t normally advocate inventing names, but if they sound nice and their is a legitimate reason for doing so (such as a meaningful family connection), how about Panelle or Panella? It sounds a little like [name]Fenella[/name] to me, and would be good in second place.
If only one middle is allowed, I would personally choose :
[name]Anne[/name] [name]Frederica[/name] nn [name]Annie[/name]
or
[name]Anna[/name] Panayio nn [name]Annie[/name], for your mother or your beloved grandmother. It would be nice for her to have one name which is all her own, too.
Other names which can give the nn [name]Annie[/name] include [name]Annaliese[/name]/[name]Annelise[/name], [name]Annabel[/name] (popular), [name]Rosanna[/name], [name]Roxanna[/name], [name]Annika[/name], [name]Anneli[/name], [name]Anthea[/name] (Greek) and [name]Calanthe[/name] (again, Greek, and also reminds me of [name]Callista[/name]. You may also like [name]Calliope[/name].
Good luck! [name]Auburn[/name]