Are the spouses considered sinful if the husband has intercourse with his wife during the daytime in Ramadan after he asked her not to fast so that they could have intercourse upon his arrival, and she obeyed him and did not fast?

If the intercourse occurred during a supererogatory (nafl) fast, there is no harm. However, if it occurred during Ramadan, it is a grave sin. If it was before dawn (Fajr), both of you incur sin and are obligated to make up the fast (qada') and pay the severe expiation (kaffarah mughalladhah). If it was after dawn, you are not required to abstain from food and drink for the rest of the day, but you both incur sin. Only she is obligated to make up the fast and pay the severe expiation for the intercourse. The preponderant opinion is that expiation is obligatory for anyone who invalidated their fast and then had intercourse, due to the general desecration of the sanctity of the month.