Mandaly. As I am fine-tuning my Kreyol Ayisyen, I have a simple question: In "Ki kote fanmi ou ye (an/nan) Ayiti?" Are both of these Kreyol words interchangeable in brackets? If not, then are there rules in Kreyol on which one to use at a given time? Mesi anpil.

This "an" acts as a preposition and translates in, of, or from
egzanp:
 M'ap rantre an Ayiti demen. → I'm coming to Haiti tomorrow.
Kote frè w la?  Li an Ayiti? → Where's your brother?  Is he in Haiti?
Mwen fèk soti an Ayiti semèn pase a. I just came from Haiti last week.
Li te gen yon bèl bag ki fèt an ajan. She had a beautiful ring made of silver.
etc...

Regarding your question... yes we might say:
Ki kote fanmi ou ye an Ayiti?
or 
Ki kote fanmi ou ye nan Ayiti?

we will also say:
Ki kote fanmi w ye Ayiti?

Dakò?

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