I'll try to answer a few questions and hopefully AZ will get a chance to drop by to expound.
"Use immunity" does not protect a witness from perjury.
*snipped*
Well, they are both probably already hostile witnesses considering neither one of them wants to be there to answer the SA's questions.
If they attempt to tell the SA what is "relevant" and dodge the question posed to them, HHJP will order them to answer it.
If they say anything in direct conflict with their prior statements/depos taken while under oath, LDB will drag out their statement or depo and read them the portion that is in conflict, thereby impeaching them. (LDB's motion cited several portions of their depos/statements that she finds relevant to the motion)
I know during the trial they would NOT be allowed to. I am assuming the same rule will apply at this hearing.
To clarify - the one who testifies first would be allowed to hear the second witness' testimony, UNLESS there is reason to think the first witness would need to be re-called to the stand