How is the estate of a deceased Muslim man to be divided when he leaves behind a Christian wife and two children from her, and a Muslim wife and one child from her?

If the aforementioned man dies as a Muslim, his Christian wife does not inherit from him. As for their two children, if they are minors (not yet adult), they inherit from him because they follow their father's religion and are ruled to be Muslims. However, if they are adult Christians, they do not inherit.

As for the division of the inheritance, if he has a Muslim wife, a Muslim child, and two children who are ruled to be Muslims, his Muslim wife receives one-eighth, and the remaining portion goes to the three children.

A minor child follows their parents in religion. So, if one of the parents embraces Islam, the minor children follow them in Islam.