What should new Muslims in prison do during Ramadan if their wives are not Muslim, and does the uprightness of the woman affect the matter?

There is no solution except to appeal to the prison administration to change the visitation time to be between Maghrib and Fajr, because sexual intercourse with one's wife during the day in Ramadan is not permissible in Sharia, and it is one of the worst things that invalidate the fast, and it necessitates expiation (freeing a believing slave, and if one cannot find one, then fasting for two consecutive months, and if one cannot do that, then feeding sixty poor people), along with repentance and making up the day. And upon you is to educate and advise with kindness.