Some families just do things that way. My own children call us Mom and Dad, but my cousin's son, from the time he could talk, called his parents and us by our first names. At first, that was a shock to me and to my children.
However, with cousins, I am not sure what would be proper - maybe something like "Cousin Carol". I believe when I was growing up, I avoided calling my parents' cousins by any name at all.

CarolM
^j^