No, if you are an O-1 you can only work in your identified job and any connected events pertaining to it.
Yes, spouses and children of an O-1 are eligible to be in O-3 status. Dependents need to show evidence proving the familial relationship. Dependents cannot be employed but may attend school.
A person may qualify for an O-1 visa if they have a level of expertise that is not common and are part of a small elite group of individuals at the top of their indicated field.
Unlike the H-1B, the O-1 has no numerical limit. There is no minimum prevailing wage requirement, although the wages offered should be what is expected for someone in a position of O-1 caliber. While premium processing is occasionally suspended for H-1B petitions, it remains available for O-1 petitions.