"How many younger siblings do you have?"

Translation: 동생 몇 명이 있어?

[KarenTse2]

Why are they using 반말?

[Chel_1215]

It is confusing at times cos you dont know when to use certain levels at certain times

[blzs92]

How about using here " 너에게 동생들이 얼마나 있어요 (있어)? "
Thanks for help.