Shalom, First you must make sure the conversion is done the right way and that she will accept the yoke of Torah and Mitzvot completely and also your kids. The actual conversion will not fix the sin rather you both need to do Teshuvah for it. To start the tikun (fixing) you must stop right away marital relations with your wife till she completes her conversion and after the conversion you have to get married according to the laws of Moshe and the Torah. By not being together till then, this will fix the sin of being together before. Wishing you great success All the best Alon Anava