A Fiancé Visa is available only to fiancés of US citizens who live outside the US. This family visa allows fiancés of US citizens to come to the US to get married within ninety days of issuance. Otherwise, fiancé status automatically expires.
Once approved, your fiancé may immediately apply for permission to work, which would be valid only for 90 days. However, after married, your fiancé would be eligible to apply for an extended work authorization at the same time as she or he files for permanent residence as an immediate relative.
Your fiancé’s children under 21 and unmarried should be included on your fiancé visa petition since a nonimmigrant visa may be available to them.