I think I would concentrate on using their own Bible:
*** Bible Citations ***
(Malachi 2:16) For I hate divorce,” says Jehovah the God of Israel,
(Matthew 5:32) However, I say to you that everyone divorcing his wife, except on account of sexual immorality, makes her a subject for adultery,
(Matthew 19:9) 9 I say to you that whoever divorces his wife, except on the grounds of sexual immorality, and marries another commits adultery.”
*** w12 5/15 p. 9 Take a Positive View of a Strained Marriage ***
WHEN MARITAL BONDS ARE THREATENED
5 Those who experience heartache in the marital relationship may wonder: ‘Is my unhappy marriage really worth saving? If only I could turn back the clock and begin again with another marriage mate!’ They may dream of breaking the bond—‘Oh, to be free again! Why not get a divorce? Even if I cannot get a Scriptural divorce, why not separate and enjoy life again?’ Instead of thinking in those terms or fantasizing about what might have been, Christians should make the best of their current state by seeking God’s guidance and following it.
6 If a Christian were to get a divorce, he or she may or may not be Scripturally free to get married again. Jesus said: “Whoever divorces his wife, except on the ground of fornication, and marries another commits adultery.” (Matt. 19:9) Here, “fornication” includes adultery and other serious sexual sins. It is vital to weigh prayerfully any thought of divorce when neither mate has been guilty of sexual immorality.
*** w08 11/1 p. 13 Do Jehovah’s Witnesses Break Up Marriages? ***
Jehovah’s Witnesses hold to Jesus’ view that adultery provides grounds for divorce. But they also strongly believe that marriages should not be dissolved for trivial reasons. They encourage their members to abide by Jesus’ words: “A man will leave his father and his mother and will stick to his wife, and the two will be one flesh. . . . Therefore, what God has yoked together let no man put apart.”—Matthew 19:5, 6.
*** w07 5/1 p. 19 par. 3 Do Not Put Apart What God Has Yoked Together ***
3 In the modern world, when some couples encounter problems, their first reaction is to end the marriage. In many lands, divorce rates are spiraling out of control. However, true Christians handle problems rather than run from them. Why? Because they view marriage as a sacred gift from Jehovah. Jesus said regarding married couples: “What God has yoked together let no man put apart.” (Matthew 19:6) Granted, living by that standard is not always easy. For instance, relatives and others—including some marriage counselors—who do not recognize Bible principles often encourage couples to separate or divorce on unscriptural grounds. But Christians know that it is far better to repair and maintain a marriage than to dissolve it hastily. Indeed, it is vital that at the outset we resolve to do things Jehovah’s way—not according to the counsel of others.
If you have been faithful in your marriage, the fact that you are no longer a "believer" does not constitute grounds for breaking the marriage. Obviously, the unselfish thing for both of you to do, is to ensure that your children have BOTH "good parents" to raise them.
Good luck,
Doc