The judge told the man not to tell the children that he was not their biological father. One day the school counselor called the man and told him the children knew and wanted to talk to him. Soo, the father went ahead and told him that he is not their father. By doing this, he violated his court order and his visitation rights were suspended.
About the biological father, the mother said that he doesn't need to jump into the picture in the middle of everything. She doesn't want him involved. If she didn't want him involved why did she screw him for so many years and allow him to father three of her four children while she was married to another man??
Forgot to add:
There was an update on the show and the ex-husband and the four children are now re-establishing a relationship.