Hi there, I also have Costain relatives.

I only know as far back as my great grandfather though.

Joseph Edric Costain, Born in Foxdale, Isle of Man on 7th of Jun, 1892.

Joseph's children:
Virginia McIntire (Costain)( Passed away )
Mary Fox (Costain)( Passed away )
Joseph Costaine ( Alive )
Elizabeth Warrick (Costain) (Passed away )
Russel Costain ( Alive )
Donna Herrlein (Costain)(Alive)

Elizabeth Warrick had 7 children, 22 grandchildren, and 8 great grandchildren. Her descendants are primarily located in Ohio, USA.