EveH on Family Tree Circles

im not sure if you go by that surname.,I'm 16 and my dads name is Graham Hansen from Invercargill. Ive been looking for our long lost sister tammy and brother Klint. We have never met or talked,all i know is their first names and not their last names,wether they went by dads names or their mums.
i think she will either be in her early 30s or late 20's.