suggie:Can I be sued.
Yes.
Of course you can be sued. All it takes is somebody who thinks they have a beef with you.
suggie:Do I need to get a release signed by the
individuals in my book even though they are
not mentioned by their real name?
Depends on what you are writing, who you are writing about, whether the people can be easily identified, and whether what you are writing will be considered by them to be detrimental to them.
For example, if your neighbor is John Smith and you write: "Yesterday, my neighbor Bob Jones sliced up a cat and fed it to his children", you'd better get a release.