I am divorced and have custody of my two children a boy of 8 years and a girl of 10 years.

Question

I am divorced and have custody of my two children – a boy of 8 years and a girl of 10 years. The father now demands custody, saying that according to the Shariah both children have to come to him as he is now the custodian according to the Shariah. I am aware of this rule of the Shariah. However, my ex-husband and his wife, both are impious. They are modernists who indulge in many haraam activities. Movies, sports, no purdah, etc. are the ways of their life. Can I deny him custody because of his un -Islamic way of life? His wife will not be able to give my children the Deeni upbringing which is so necessary. I homeschool my children. The father will place them in some public school.