Native speakers will understand both questions, but I think using the word “siblings” sounds more formal, while the phrase “brothers and sisters” sounds more informal. In English, we don’t have formal and informal versions of words like they do in other languages - for example “tu” versus “vous” in French, but we do have a general sense of formal versus informal ways of saying things. Both versions of the question are perfectly correct and understandable. It just depends on how you want to be perceived by the person you are speaking to.