Would you mind answering my questions please?
If we wanna ask about the relation between you and someone else how we can ask this?For example if they are your cousin or niece or nephew and so on.

Another question is about If you gonna have an celebration and I'm gonna ask you what is the reason of having that,is it correct to say what is the celebration about?

Question

Would you mind answering my questions please?
If we wanna ask about the relation between you and someone else how we can ask this?For example if they are your cousin or niece or nephew and so on.

Another question is about If you gonna have an celebration and I'm gonna ask you what is the reason of having that,is it correct to say what is the celebration about?

Answer

1) How are you related?

2) If you ask "what is the celebration about" everyone will understand you perfectly. But it is more common to ask "what are you celebrating?" or "what's the celebration for?"

Answer

I agree with all of the above. You could also say, "What's the occasion?"