The correct answer to the question, "Do you have brothers or sisters and how old are your brothers and sisters?" would be to provide the names and ages of your siblings, if you have any. For example:
"I have one sister named Sarah, and she is 28 years old."
Or, if you have multiple siblings:
"I have two brothers and one sister. My older brother, Tom, is 32 years old, my younger brother, Alex, is 24 years old, and my sister, Emily, is 30 years old."
Simply state the number of brothers and sisters you have, followed by their names and respective ages, if you have this information available.