I have designed an educational product which uses the likenesses of people throughout history. What can I legally do or what do I need to do?

As a general matter, the likenesses of long-dead people may be used for commercial purposes without the consent of their estates. There are some limited post-mortem "publicity" rights regarding certain celebrities granted under state law, but these rights generally do not endure for more than 70 years after death. See California’s Publicity Rights statute, CAL. CIV. CODE § 3344.1. An attorney can assist you in working through the issues involved.