Father: Orodreth (Ondarato) Second King of Nagothrond
Siblings: Ereinion Gil-Galad (Rodnor) ¿?
(note that the family relations here expounded are a mix of the Silmarillion verse and the later notes of Professor Tolkien, as in the Silmarillion Finduilas is quite clearly the daughter of Orodreth and it is the clearer parentage she has; and on the other hands in later works she appears as the plausible sister of High King Gil-Galad when he stems form the House of Finarfin, contrary to the genealogies of the Silmarillion).
Fiduilas Faelivrín was an elven princess of tragic fate. Even if by some versions of the mythos she is Orodreth's daughter and Finrod Felagund's niece, in some, she is Angrod's grandaughter, and sometimes even Gil-Galad's sister (when he belongs to the house of Finarfin), she always remains the princess of Nagothrond and the gentle elven princess who falls helplessly in love with Túrin Turambar even against her better judgement and dies in the sack of Nagothrond. The insecapable nature of her love for the tempestuous mortal man, and her inability to reciprocate the love her friend Gwindor has for her, even if she wishes she could change circumstances, make her story tragic long before orcs take her captive and slay her in the sack of the acient Halls of Felagund. As she is taken away she calls for Turin, who stands paralyzed in a trance in front of the dragon Glaurung and does not hear her, and cannot rescue her; and it spells her doom.