Off the top of my head, without benefit of seeing the subpoenas for the depositions (which, as in the case of Amy, mentioned above, would tell me a lot about what Baez wants to see, if he's sought written materials, too, via a subpoena deuces tecum,) I believe JBaez is intending to lock in potential key witnesses to their stories:
(1) as to Kronk, deputy, Hoover, DC, etc., it's all about when/how/why they noticed/discovered anything relevant to the case. If JBaez can poke even a single hole in Kronk's version of the events re: finding Caylee, well, you can only imagine where JBaez would try to take that during a trial; and
(2) as to the guards at the jail, it will be all about the specifics concerning Casey's reaction to the news on December 11, 2008, and possibly his and Casey's reactions when he was allegedly crying on whatever date that supposedly took place. If JBaez can find anything upon which to claim that Casey's rights were violated, he'll be moving to suppress any such testimony and/or evidence stemming therefrom.
So I don't think it's so much as what JBaez "expects" them to say as it is he needs to know what they will say so he can plan what to do next.
He's obviously worried about something - so he's got to see if it's going to be something he can suppress, or whether he's going to have to go to trial and deal with it in front of the jury.