The requirements for applying as a married couple or an individual are different. As a married couple it would be easier to meet the requirements of sufficient Existing Financial Resources and Passive Income.
In particular, the qualifying thresholds per person are proportionally lower when applying as a couple than when applying as separate individuals.
Therefore, in order to apply as a married couple and/or for a dependent the Italian Consulate requires valid evidence of your family relationship. Non-Italian marriage certificates or birth certificates that are not issued from the country where the Consulate is located need to be translated into Italian and validated (e.g., legalized, apostilled) before you submit them. Check with the local Consulate for their specific policy.
You will also need a FBI Criminal Background check for each applicant (not mandatory but highly recommended).