There is an Oatman geneology on the web athttp://www.sentex.net/~cdoatman/oatman.html
It contains some history about the Oatman family at the time of Olive Oatman.
Go the Index link, and then click on the name Royse. That should provide you with a good starting point, anyway.
There is also a book entitled, "The Captivity of the Oatman Girls." I have never seen the book personally, but I have frequently heard about it.
Hope this helps!