Legal Question in Intellectual Property in California

Re: Are well known life stories of celebrities considered public domain?

This is an excellent question. Congratulations on asking it now, before you've spent a great deal of time and effort on creating a screenplay. Unfortunately, too many writers in your situation do all their work first and then find out they can't use some or all of it.

The answer to this question, however, is not so easy. Generally, facts are not copyrightable and can be used freely. Expressions of ideas or facts ARE protectible and you would need permission. For instance, an event that is widely reported and accepted as true is okay, but direct quotations of what someone said would probably be protected.

As for dealing with heirs: generally a person's right to publicity and privacy die with the person. In the case of some celebrities, however, the right of publicity continues after their death. In California, there is a system of registration to protect such rights of publicity (most other states do not have such a system). So, it depends on who the celebrity is, and you would be wise to discuss your plans in detail with a competent entertainment/intellectual property attorney.

Re: Are well known life stories of celebrities considered public domain?

If you are exclusively using "facts" from other books to create your own original screenplay, it is unlikely that you are infringing any copyright subsisting in those other books that provided a basis for your research. However, if you are reproducing any original expression from those books, you may need to get a copyright release and/or license from the authors to avoid infringement, depending on the nature and extent of any material you reproduce.

As for the celebrity's estate, you may need to seek permission, as they may be entitled to prevent your screenplay depiction under rights of publicity that inure to the benefit of famous people.