Quick question need input quick

[T0052SC]

I have a pretrial hearing coming up next week.  I don't know what takes place at the pretrial and am a little scared of what may happen.  I have had a PI working on the case and the PI had the STBX arrested for leaving the kids in a unattended vehicle while shopping (kids 3 and 5).  The police department exposed my PI to my STBX and now my STBX is calling the police left and right to report suspicios vehicles even though the PI hasn't worked the case in over two weeks.  My attorney even got a call from a state trooper about all the reports.  My PI says that they need to come to the pretrial hearing with me because the STBX and her attorney will most likely try to pull something there and try to get the kids taken away from me or restaining orders.

My questions
What goes on at a pretrial hearing?
Can the STBX and her attorney pull anything at the hearing or is it to just evaluate time for trial and evidence and witnesses?
Is it a good idea to have the PI there?
What can I expect and do?