* Eres hijo único o Tienes hermanos: This phrase is asking whether someone is an only child or has siblings.
Here are a few ways to say it in English:
* Are you an only child or do you have siblings? (This is the most direct translation.)
* Do you have any brothers or sisters? (This is a more common way to ask.)
* Do you have siblings? (This is a shorter and more informal way to ask.)