Dear Matt:

We can never know if someone is going to hell. The only way to get to hell is to die in a state of mortal sin.

Be be guilty of mortal sin once must commit a grave sin, must know that it is grave sin, and must have freedom of consent.

You don't say if your father is Catholic. If he is Catholic then he cannot be validly married without an annulment of the first marriage. Even if annulled, getting married outside of the Catholic Church is also invalid.

For a divorced Catholic who wants to marry again, all previous marriages must be annulled or have any other impediments resolved and the new marriage be in the Catholic Church.

If the Catholic does not do these things, then their new marriage is not valid and they are not married in the eyes of God. This means they are living on concubinage (living as married when not married) and adultery. These are grave sins.

Anyone living in grave sin is barred from the Sacraments and is indeed risking their soul to hell. But whether or not such a person will actually go to hell depends upon if they are fully culpable for the grave or have a "diminished capacity" due to situations such as mental illness, immaturity, etc. Only God can truly know the level of culpability of a person and thus only God can know if a person is truly in mortal sin when they die and therefore go to hell.

Bottomline: You do not give many details, but if your father is Catholic and remarried without an annulment, and/or remarried outside of the Catholic Church then he is not married in the eyes of God and is committing adultery. This places his soul at risk.

Pray for him. We will certainly be in prayer for him.

God Bless,
Bro. Ignatius Mary