Lilac isn't my favorite floral name, but there's nothing really wrong with it either.
Margot Jane Lilac is lovely.
I'm not very good at double mns, so I'll confine myself to fn / mn, OK? How about:
Miranda LilacIsidora LilacDaphne LilacVivien LilacJosephine LilacSophie LilacJacintha Lilac (although
Jacintha = hyacinth. Is this too floral?)
Mary LilacDelphine LilacViveca
LilacAnna LilacFreya /
Freja LilacAilsa LilacDeirdre LilacFiona LilacElsa LilacCarys LilacSylvia /
Sylvie Lilac
Are there any you like?