Start here.
First Preference EB-1 - This preference is reserved for persons of extraordinary ability in the sciences, arts, education, business, or athletics; outstanding professors or researchers; and multinational executives and managers.
Second Preference EB-2 - This preference is reserved for persons who are members of the professions holding advanced degrees or for persons with exceptional ability in the arts, sciences, or business. Labor certification is required, unless applicant can obtain a national interest waiver (See the “Labor Certification” link to the right for more waiver information.)
Third Preference EB-3 - This preference is reserved for professionals, skilled workers, and other workers. (See Third Preference EB-3 link on left for further definition of these job classifications.) Labor certification is required.
Fourth Preference EB-4 - This preference is reserved for “special immigrants,” which includes certain religious workers, employees of U.S. foreign service posts, retired employees of international organizations, alien minors who are wards of courts in the United States, and other classes of aliens.
Fifth Preference EB-5 - This preference is reserved for business investors who invest $1 million or $500,000 (if the investment is made in a targeted employment area) in a new commercial enterprise that employs at least 10 full-time U.S. workers.
I can't imagine labor certification being granted for real estate agents, so (other issues aside) EB-2 and EB-3 don't appear realistic. I'm not seeing how the work you want to do fits under EB-1 or EB-2. You've already suggested that you can't qualify for EB-5.