Hi - you really need to see the wills or administrations for each generation of the family. Also check out the land records to see what property was held, bought, sold mortgaged etc. Often there were several families in the one parish with the same name. Also for the period circa 1700 not all the Parish Registers have survived, so the may be other individuals around whose children, marriage etc does not appear in the IGI. See comments on the IGI in the latest edition of 'The Manx Family Tree'

Nigel