In English there is siblings, in German Geschwister. To the best of my knowledge, French does not have a single word but rather uses (les) frères et sœurs construction.
So does French lack indeed a single word as I think, for such a basic situation? Can we use sibling(s) as it is in French?
There is a term: "fratrie", but it lacks the non-gender feeling that siblings has. I think that's why it's not used as often as in other languages, because of this bias.
Still "fratrie" encompasses brothers and sisters in a family.
There is a word : adelphe. It is not really used anymore, but it has exactly the same meaning as sibling in english.
Sibling used to mean relative, brothers-and-sisters is a modern evolution of this ancient germanic word.
Geschwister has a feminine bias (Schwester).
Fratrie has a masculine bias (frère).
All these words, included the French word contrary to your supposition, are used to mean brothers-and-sisters, but not the Greek φρατρία the meaning of which being more tribe than family (another evolution of the Indo-european root).
Complément : il y a quelques attestations du mot "sibling(s)" en francais (ngram). Selon https://fr.wiktionary.org c'est rare. Le même lemme indique que germain est plus courant (pour l'anthropologie ; merci @Gilles !).
