Generally not.  That is why so many defendants do not wish to take the stand in defense of their case.  Their "prior bad acts" can not be disclosed or used against them unless the defendant places their credibility in to issue, and that happens when they take the stand and testify on their own behalf.  As for the witnesses, they are sworn to tell the truth.  If they are caught lying that can be perjury.  But if there is a jury in place they will hear the lies and it will go to the weight of the evidence.  In other words, they will decide the case balancing all the testimony given. Good luck.