If you include COSTEAN/COSTEN they are spread between a number of parishes on BL's burial index, although the majority seem to be in Arbory. There were a few families in Maughold, especially during the 1600s/1700s, down to Helen Hawthorne the daur of Edward Ellis Costain & Lily Margaret Corteen bapt in Dhoon Church in the 1930s.
In early Maughold wills it is sometimes very difficult to see the difference between Costean and Cortean (and variations).

The wills index also shows a variety of parishes for Costain. Not many transcripts attached at the moment [lawsonsiom.freevar.com/wills/co5-will.html] but I have nearly 30 (not mine) ready to go on when Ian gets through the backlog - these are mainly from the 1600s and early 1700s, and again mainly from Arbory but with a few from Maughold, Santan, Lezayre, and Malew.

Sue