As with the expression of possession in general, there are two ways to express that one has siblings.
The У мене form. As in: У мене є брат , literally [In me there-is brother] The Я маю form. As in: Я маю брата, literally [I have brother]
It is more typical to use the first form. Thus to express [I have one brother and one sister], Ukrainians say:
У мене є один брат і одна сестра.
To express that one does not have a sibling, use the word немає, which means [there is not].
У мене немає брат means [I don't have a brother].
У тебе є брати або сестри? is the informal version of the question, [Do you have any brothers or sisters?]. Note that this sentence translates literally to [In you there are brothers or sisters?].