Help understanding preliminary hearing?

My brother has a preliminary hearing in Tennessee tomorrow and I'm curious at to what will happen. The charges against him are aggravated DUI and 3 counts of felony wanton endangerment against police officers stemming from the drunk driving-although no one was injured in any way during the incident. He does have an attorney, but he really hasn't given us details because he doesn't know what will happen. My brother has already paid him $6,000 so it would be nice if he had given us some information. What I would like to know is, what is are the general things that happen at a preliminary trial, will anyone, like the police officers be called to testify, and could he be held on bond, and if so, what would be a fair estimate of the bail they would ask? Thanks so much for any help.