Does what Ibn Taymiyyah mentioned mean that whoever experiences a slight doubt within themselves, despite possessing strong faith in Allah and the Messenger, is not considered a disbeliever? And must one of the spouses inform the other if they apostatized and then repented?

All sins are branches of disbelief, just as all acts of obedience are branches of faith. The branches of faith and disbelief are of two types: verbal and practical. Among the verbal and practical branches of faith are those whose removal necessitates the removal of faith itself, and similarly for the verbal and practical branches of disbelief. Doubt does not apply to this rule, but obsessive whispering (waswasah) differs from doubt. What you are experiencing is obsessive whispering, and these whispers do not make you a disbeliever or a sinner. We advise you to adhere to supplication, humility, distraction from these whispers, and to consult a trusted psychiatrist.