What is the appropriate adjective for the masculine noun invitados?

The appropriate adjective for the masculine noun "invitados" is "invitados" itself when used in its plural form. If you are looking for a specific adjective to describe the guests, it would depend on the context, such as "importantes" (important) or "cordiales" (cordial). The adjective must also agree in gender and number, so it should be in the plural masculine form.