All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is no doubt that abandoning the prayer is one of the grave major sins but there is a difference of opinion among the jurists on the ruling on a person who abandons the prayer. Most of them are of the view that such a person does not go out of the fold of Islam. This is the view chosen by Ibn Qudaamah from the Hanbali School of jurisprudence, contrarily to the well-known opinion in his School of jurisprudence. So, you may act according to his view.
In support of his opinion that the person who abandons the prayer does not go out of the fold of Islam, he made the following statement: “…because this view is the consensus of the Muslim scholars, as we do not know at any given time that a person who abandoned the prayer was not washed after his death, or that the funeral prayer was not conducted on him, or that he was not buried in a Muslim graveyard, or that his heirs were prevented from inheriting from him; also, he himself was not prevented from inheriting from the person whom he is entitled to inherit from, and no married couple was separated because either of them abandoned the prayer, while there are so many people who used to abandon the prayer. If such a person [i.e. the person who abandons the prayer] was considered a disbeliever [i.e. went out of the fold of Islam due to not performing the prayer], then such rulings would all have been confirmed against him.” For more benefit, please refer to Fataawa 83943, 85264 and 86918.
Based on this, your marriage is valid, so each of you should have good marital relationship with the other, and you should perform good deeds, become righteous in the future and be keen on acquiring beneficial Islamic knowledge.
On the other hand, if it becomes evident to you that your father is still abandoning the prayer, then you should advise him in a gentle manner, or you may seek the help of whoever may influence him to do so. For more benefit, please refer to Fatwa 21794.
Allaah Knows best.