From what I've gathered I may need to use several spells to calm this mess. 1). Just in case: a spell breaker if there IS a negative spell in place. 2) removing bitterness, anger, and "social ineptitude" from ex wife (who btw is Catholic) 3) finally, for children to realize their father's love is there even w a new significant other.
Magic can't be used to solve every single problem you face in life. Life Problems are tests of character ( in my opinion ). Have you ( or any others involve ) tried just a simple talk with both the children and the ex wife?