The other day I stumbled over the word "nibling", i.e. a gender-neutral word for niece and nephew: https://www.nbcnews.com/feature/nbc-out/jennifer-lopez-shares-video-about-transgender-nibling-brendon-n1237838. The term was coined in the 1950s but is only recently gaining more momentum: https://www.merriam-webster.com/words-at-play/words-were-watching-nibling.

I realised that this term doesn't exist in German. We could only refer to niece and nephew as niece and nephew but don't have a gender-neutral form like nibling. We do have the word "sibling" though:

brothers = Brüder

sisters = Schwestern

siblings = Geschwister

Now if you say, "nibling" isn't a real word but "sibling" has always been around, you might be surprised that using the word "sibling" in the sense of "brothers and sisters" is relatively new and only dates back to the beginning of the 20th century: https://www.etymonline.com/word/sibling. Originally, a sibling was just someone who was a relative belonging to the same "sibb". Why did the need for such a term arise? Wiktionary claims: "The term apparently meant merely kin or relative until the 20th century when it was utilised in a way that aided the study of genetics, which led to its specialized use. For example, the OED has a 1903 citation in which "sibling" must be defined for those who don't know the intended meaning." (https://en.wiktionary.org/wiki/sibling#English)

In many languages the word sibling doesn't seem to exist. In French you just say

"frères et sœurs" (brothers and sisters) and in Spanish "hermanos", which can mean either brothers or siblings but definitely has only a male form ("hermanas" are sisters). Interestingly, in Spanish "padres" denotes both "fathers" and "parents", so there is no actual word that is either neutral or visually includes the moms as well. In Chinese you can say "父母" (father, mother) for parents" and "兄弟姐妹" for "siblings" which literally means "elder brother, younger brother, elder sister, younger sister".

Interestingly, in Turkish there is only one word for brother, sister and siblings: kardeş. You can specify by saying erkek kardeş (man sibling), kız kardeş (girl sibling) and kardeşler (siblings). For parents there is the word "ebeveyn" that derives from the Arabic الأبوان which is a dual form of أب (father), so it's "two fathers = parents" and similar to "padres" in Spanish. But another Turkish word for parents is "anne baba" which means "mom dad".