Is it insulting to call a full professor Dr. Firstname Lastname in a non-academic event program?
For most people, insult and offense comes more from lack of care and respect than from mistakes.  I would thus recommend the following procedure:


Prepare a draft, making your best guess for each speaker based on their web presence.
Send out the draft agenda to all speakers, saying that this is the draft and you'd like corrections in case you have made mistakes in how anybody is listed.  (You probably want to run the schedule by them anyway for other purposes as well.)
Make any corrections requested by the speakers.


This way, if you get anything wrong, you're doing it in private, acknowledging possible errors, and giving them a chance to correct you in private as well.  It will be a rarely sensitive person or an unusually significant mistake that will cause offense in this way.