The author of my dad's autobography wants half the royalitites. She has been paid all along for her writing. I say she should nothing but the fees for her writing.
All the agreements and understandings should be well defined (in writting !) in advance and should be very clear to both parties. In that way one avoids arguements and misunderstandings. If it had not been done so all is open for arguements / demands / fights ........ Having said that, if she receieved money for doing the job it is not fair to ask for royalties too.